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Lifetime traits comparison between annual and accelerated lambing systems for dairy ewes
Livestock Science 101 (2006) 180 – 190 www.elsevier.com/locate/livsci
Lifetime traits comparison between annual and accelerated lambing systems for dairy ewes U.M. El-Saied a,*, L.F. de la Fuente b, F. San Primitivo b b
a Animal Production Research Institute, Nadi El-Said St., Dokki, Giza, Egypt Departamento de Produccio´n Animal I, Facultad de Veterinaria, Universidad de Leo´n, 24071 Leo´n, Spain
Received 2 June 2005; received in revised form 18 October 2005; accepted 1 November 2005
Abstract Two sets of data with a sum of 6318 lactations for 1391 Spanish Churra ewes, belonging to 10 flocks were used to study phenotypic, genetic and system efficiency parameters of lifetime traits in annual and accelerated lambing systems. The study included four life span traits, three productive traits and two reproductive traits. Trait averages for both milk yield and revenues from sold milk and weaned lambs were calculated per-day of lifetime, productive life and useful life. The animal model included flock and ewe birth year as fixed effects. Both effects contributed significantly to variation in most traits in the annual system while birth year was non-significant for most variables of the accelerated system. Milk production level was included in the model to analyze life span traits. It contributed significantly to variation in all life span traits in both systems. Means for productive and life span traits were significantly higher in the accelerated system compared with the annual system. The average interval between successive lambings was significantly shorter in the accelerated system, while age at first lambing was significantly lower in the annual system. Except for age at first lambing, heritability estimates were clearly lower in the case of the accelerated system (0.02 to 0.20) than in the annual system (0.08 to 0.45). Genetic correlations among traits were also lower in the case of the accelerated system. Failure to lamb three times in two consecutive years and the varying reproductive management among flocks in the accelerated system may be responsible for the differences in genetic results between the two systems. Improving reproductive performance is necessary, especially for the young high yielding ewes in the accelerated system. Management to ensure high fertility, especially among young ewes, would be of more importance than removing nonlambing ewes. D 2005 Elsevier B.V. All rights reserved. Keywords: Genetic parameters; Lifetime traits; Lambing systems; Dairy ewes
1. Introduction * Corresponding author. Present mailing address: Departamento de Produccio´n Animal I, Facultad de Veterinaria, Universidad de Leo´n, 24071 Leo´n, Spain. Tel.: +34 987 29 12 88; fax: +34 987 29 13 11. E-mail address: [email protected] (U.M. El-Saied). 0301-6226/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2005.11.003
As is the case for numerous dairy breeds in several countries, genetic selection in Churra dairy ewes has placed primary emphasis on milk yield for many years.
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In the last 5 years, however, there has been increased interest for selecting additional traits to increase profitability including protein percentage and udder and type traits. Longevity, or length of lifetime, is a composite trait of production, health and reproduction (Mulder and Jansen, 1999). Long lifetime indicates good health and fertility, allows the animal to achieve its maximum productive capacity, contributes to reducing replacement and treatment costs, means fewer losses due to involuntary culling and increases the scope of voluntary culling (Dekkers, 1993; Jairath et al., 1994; Boettcher et al., 1997). Because of its effect on economic performance, lifetime has been seen as a trait of interest for animal breeders, in general, and dairy breeders in particular (Allaire and Gibson, 1992; Dekkers et al., 1994; Pe´rez-Cabal and Alenda, 2003). Profit maximization on dairies is dependent on the ability of the herd management program to maximally reduce the acquisition and maintenance cost of animals throughout their lives (Lormore and Galligan, 2001). The annual lambing system is very common in ovine breeds. However, Churra dairy sheep breeders apply either the classic annual lambing system or the accelerated system of lambing three times in 2 years. Therefore, life span traits (productive life, useful life and lifetime score) and yields of milk and lambs during the lifetime of the ewe and consequently the final profit are expected to vary from one system to another. The objective of this work was to compare estimates for phenotypic and genetic parameters and some efficiency parameters of various lifetime traits in Churra dairy ewes according to the lambing system (annual or accelerated), discuss both the possible
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reasons behind the expected differences and future possibilities of improvement.
2. Materials and methods 2.1. Data Data were obtained from the National Association of Spanish Churra Breeders (ANCHE, Palencia, Spain) and were collected between 1990 and 2003. Table 1 presents a summary of the data analysed in this work. Two sets of data were considered. The first set considered six flocks applying an annual lambing system while the second contained four flocks applying an accelerated system to lamb three times in 2 years. In both sets of data, records included dates of birth, lambing, dry off and culling and yields for milk and lambs. All flocks were enrolled in the nucleus scheme of the Spanish Churra dairy breed. Late gestation ewes are usually kept together in a single yard; many of them give birth to multiple lambs. In order to prevent wrong dam-lamb assignation, pedigree control is regularly done by the Department of Animal Production I, University of Leo´n (Leo´n, Spain) using DNA genetic markers on sample individuals from all those flocks enrolled in the nucleus scheme of Churra breed. All ewes were daughters of AI sires and were artificially inseminated themselves; therefore, complete pedigree information was available over the study. Many genetic links existed among the flocks due to extensive use of AI. There were management similarities between annual and accelerated lambing systems. In both systems, ewes were permanently
Table 1 Description of data for lifetime performance traits under annual and accelerated lambing systems Item
Annual system
Accelerated system
Ewes with records, no. Lactations, no. Sires, no. Daughters/sire, range Flocks, no. Connected flocks by each sire, range Dams, no. Dams with records, no. Parities/ewe, range Years of birth of the ewe
838 3150 63 1–81 6 2–6 691 84 1–10 1990 to 1995, inclusive
553 3168 65 1–55 4 2–4 464 39 1–14 1990 to 1995, inclusive
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housed indoors at night and grazed during the day under stable management and nutritional conditions. Lambing usually took place during autumn (39% in annual system and 45% in the accelerated one) and spring (38% in annual system and 41% in the accelerated one) and flock size is around 400 ewes. More details on management of Churra flocks were previously reported (Gonzalo et al., 2005). In both systems, the suckling period averaged 30 days and ewes were milked for approximately 120 day after weaning. Lambs were typically slaughtered after weaning to meet the market demand. Milk yield per lactation was estimated by ANCHE using a set of test-day records taken at monthly intervals following an alternative a.m.–p.m. recording scheme. Fat and protein in milk were measured by the automated infrared absorption spectrophotometry method (Milk-o-Scan; Foss Electric, Hillerød, Denmark) by the analysis service of the milk-testing program for the local government. According to the testing program applied for Spanish ewes in both annual and accelerated lambing systems, the first test day record was obtained at least 3 days following weaning, between the 31st and 75th day postpartum, and at approximately monthly intervals thereafter. The interval between lambing and first test day averaged 45.69 and 45.99 days in annual and accelerated systems, respectively. Details on yield recording of Churra ewes have been reported by El-Saied et al. (1998, 1999). All ewes had to have consecutive lactations, starting with the first. Ewes were born between 1990 and 1995 and therefore the youngest ewes had at least 9 years of opportunity of life. Lambing took place between 1992 and 2003, inclusive. Ewes were kept in the same flock throughout their lives. An age at first lambing of between 12 and 36 months was required and the lambing interval was restricted to between 180 and 599 days. The end of data recording was due to mortality, accidents, health disorders or low production. Unfortunately, reasons for culling were not recorded for each individual ewe. For modelling purposes, all ewes had to remain in the same flock throughout their lives. 2.2. Traits The present study included two productive traits: total milk yield during lifetime and number of lambs
sold at weaning during the lifetime of each ewe. Ewe lifetime productivity from both milk and lambs were transformed into their equivalent sum of revenues according to their prices. The milk and lamb pricing system did not change during the time of data recording. Lambs were always sold after weaning (3 to 4 weeks of age) to be slaughtered at 10–15 kg of live body weight. Churra milk is exclusively made into cheese. Therefore, milk composition in protein and fat was the determining factor of yield and quality of the final product and consequently of milk price. Detailed information on this aspect is available in the work of Othmane et al. (2002). In the present study, revenues from milk were calculated as a function of milk yield and, protein and fat content. There were no differences in milk pricing system between the two lambing systems. Average prices were 6.3 Eurocent/l of milk and 48 Euro/lamb at weaning. Both Churra cheese and Churra lambs have a Denomination of Origin in the region of Castilla-Leo´n, Spain. Reproductive performance traits included: 1) age at lambing and 2) average interval among consecutive lactations during lifetime of each ewe. Literature presents various measures for life span. Due to the lack of research work on lifetime performance for dairy ewes, it was decided to evaluate several lifetime performance traits to completely describe ewe lifetime. Thus, complete observations were required and this is only possible for ewes with recorded culling dates (i.e. no censored records were present). The study considered 4 variables related to the life of the ewe including: 1) total lifetime (number of days between birth and culling), 2) productive life (length of time between first lambing and the last dry date), 3) useful life (total number of days in milk (DIM) during lifetime) and 4) lifetime score, i.e. the number of lactations a ewe survived. Dekkers (1993) mentioned that length of productive life is a trait of major economic importance as it combines productive and reproductive aspects excluding age at first parity. Two intervals of time that are unprofitable from a milk production standpoint are the period from birth to first parturition and dry periods (Lormore and Galligan, 2001). These periods represent non-productive days that reduce profit of production per day of life. For that reason, other measures for life span were
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added that considered both productivity and life span. These measures included: 1) milk/day for each of lifetime, productive life and useful life; and 2) revenues from milk and lambs/day for lifetime, productive life and useful life. 2.3. Statistical analysis Genetic parameters were estimated within each set using REML and the VCE 4.0 software (Groeneveld and Garcı´a Corte´s, 1998) with the following multipletrait animal model: Yijkl ¼ Fi þ Y Bj þ Ak þ eijkl where: Yijkl = Productive and reproductive lifetime traits (for complete definition of all traits, please Table 2 Least squares means and standard errors (SE) of lifetime performance traits by lambing system effect Trait1
LT, day PL, day UL, day TMY, l M / dLT, l M / dPL, l M / dUL, l Age1L, d Lifetime score Interv2 Lambs TRLT, Euro R / dLT, Euro R / dPL, Euro R / dUL, Euro
Annual system
Accelerated system
Mean
Mean
b
2069 1099b 553b 582b 0.25a 0.51a 0.95a 615b 3.9b 330a 5.7b 652b 0.29b 0.58b 1.07a
SE 33 32 16 20 0.01 0.01 0.10 7 0.1 2 0.2 21 0.01 0.01 0.01
a
2354 1316a 721a 674a 0.27a 0.53a 0.90b 652a 5.1a 294b 7.3a 789a 0.32a 0.63a 1.09a
SE 44 43 21 27 0.01 0.01 0.01 10 0.1 3.1 0.3 28 0.01 0.01 0.01
1 LT = Lifetime; PL = productive life; UL = useful life; TMY = total milk yield; M / dLT = milk/day of lifetime; M / dPL = milk/day of productive life; M / dUL = milk/day of useful life; Age1L = age at first lambing; Lifetime score = number of given parities during lifetime; Interv = average interval between successive lambings; Lambs = lambs sold at weaning during LT; TRLT = total revenues from milk and lambs during lifetime; R / dLT = revenue from milk and lambs/day of lifetime; R / dPL = revenue from milk and lambs/ day of productive life; R / dUL = revenue from milk and lambs/day of useful life. 2 Number of analyzed records for average interval between successive lambings was 801 and 523 for first and second files, respectively. a, b: Means in a row with different superscript differ ( P b 0.05).
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refer to Table 2); F i = Fixed effect of flock i (6 levels in the annual system data and 4 levels in the accelerated system data); YBj = Fixed effect of year of birth j (6 levels in both cases); A k = Random additive genetic effect of individual k; e ijkl = Random residual effect. The model described above was a linear model. In theory, survival analysis is a more proper statistical method for analysis of lifetime traits because it deals properly with the typically skewed distributions of the data and can account for censored records. However, the use of the linear model was justifiable in this work. First, only uncensored ewes were used. Second, previous results for dairy cows (Jairath et al., 1994) indicated that REML estimates from a linear model can be of practical use even when normality does not hold. Genetic selection in Churra dairy ewes has placed primary emphasis on milk production for many years. Therefore, life span traits are expected to be largely affected by milk production level. In this work, milk/day of useful life was added to the abovementioned model as a fixed effect with five levels to analyse life span traits (lifetime, productive life, useful life and lifetime score). The five levels were determined as a function of mean and SD of milk/day of useful life as: V 0.64, N0.64 to 0.78, N 0.78 to 1.08, N1.08 to 1.22 and N 1.22 l of milk/day of useful life, respectively. Each year was divided into four seasons: January through March, April through June, July through September and October through December. The results demonstrated non-significant effect of season of birth of the ewe on all traits (Table 3). Therefore, season effect was excluded from the mixed animal model. All known relationships among individuals were considered in the animal model. Phenotypic parameters were estimated by GLM and VARCOMP procedures of SAS (SAS, 1998).
3. Results and discussion We combined in a first analysis data from both systems where lambing system was added as a fixed effect to the phenotypic model in order to compare least squares means for lifetime performance traits in annual and accelerated lambing systems. The results are given in Table 2.
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Table 3 F value and significance by lambing system (RS), flock (FL), ewe year of birth (YB), ewe season of birth (S) and milk production level (PL) on lifetime performance traits under annual and accelerated lambing systems Trait2
F value and significance1 Annual system
LT, day PL, day UL, day TMY, l M / dLT, l M / dPL, l M / dUL, l Age1L, d Lifetime score Interv Lambs TRLT R / dLT R / dPL R / dUL
Accelerated system
FL
YB
S
PL
FL
YB
S
PL
16.47*** 10.72*** 15.26*** 18.05*** 28.07*** 28.19*** 27.27*** 21.80*** 16.99*** 9.53*** 12.15*** 16.54*** 22.78*** 16.89*** 13.15***
12.65*** 5.79*** 5.62*** 2.95* 3.06*** 1.90NS 4.15*** 12.42*** 6.38*** 0.65NS 4.65*** 3.65*** 2.35* 1.65NS 2.82*
1.61NS 1.41NS 1.68NS 1.54NS 1.39NS 0.37NS 0.42NS 2.03NS 1.39NS 0.65NS 0.71NS 1.29NS 0.86NS 0.57NS 0.26NS
46.70*** 41.50*** 43.11*** – – – – – 35.15*** – – – – – –
1.10NS 11.19*** 17.09*** 20.86*** 33.56*** 3.18* 5.26*** 4.43*** 17.62*** 14.06*** 22.55*** 22.62*** 42.38*** 2.39NS 4.58***
1.61NS 1.00NS 0.95NS 1.36NS 0.80NS 0.35NS 1.48NS 3.86*** 1.12NS 0.97NS 1.57NS 1.31NS 1.06NS 0.64NS 2.65*
3.15* 2.03NS 1.62NS 2.23NS 0.51NS 0.78NS 0.68NS 8.08*** 1.93NS 1.88NS 1.87NS 2.15NS 0.34NS 1.44NS 0.70NS
5.62*** 7.17*** 9.73*** – – – – – 7.83*** – – – – – –
1
*** = significant at P b 0.001, * = significant at P b 0.05, NS = non-significant. LT = Lifetime; PL = productive life; UL = useful life; TMY = total milk yield; M / dLT = milk per day of lifetime; M / dPL = milk per day of productive life; M / dUL = milk per day of useful life; Age1L = age at first lambing; Lifetime score = number of given parities during LT; Interv = average interval between successive lambings; Lambs = lambs sold at weaning during LT; TRLT = total revenue from milk and lambs during lifetime; R / dLT = revenue from milk and lambs/day of lifetime; R / dPL = revenue from milk and lambs/day of productive life; R / UL = revenue from milk and lambs/day of useful life.
2
tended to keep milking them until they got pregnant resulting in a significantly longer useful life and consequently a significantly lower milk/day of useful life compared with annual lambing system ewes. Fig. 1 shows survival curves for Churra ewes in annual and accelerated lambing systems along with age of ewes. A better survival rate was expected in the annual lambing system due to the stress of frequent lambing on ewes in the accelerated system. However, Survival percentage
As expected, all life span traits (lifetime, productive life, useful life and lifetime score) were significantly higher in the accelerated system than in the annual one. Percent increase in these traits averaged 20% (ranging from 12% for total lifetime to 23.5% for lifetime score). Also, total milk yield produced during ewe lifetime, lambs sold at weaning during ewe lifetime, and milk and revenues/day for both lifetime and productive life were significantly higher in the accelerated system. As also expected, the average interval between successive lambings was significantly shorter in the accelerated lambing system. However, age at first lambing was significantly lower in the annual lambing system. Milk/day of useful life was significantly higher in the annual system and revenues from milk and lambs did not differ significantly between the two systems. Due to the negative relationship between high milk yield and reproductive performance (Robinson et al., 2002, in press), some higher yielding ewes in the accelerated system failed to get pregnant at the right time according to the accelerated system point-of-view. Therefore, breeders
100 80 60 40 20 0
2
3
4
5 6 Age (years)
Annual System
7
8
9
Accelerated system
Fig. 1. Survival curves for Churra ewes in annual and accelerated lambing systems along with age of ewes.
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the results showed that only 63% of the annual system ewes survived to the fourth year of age compared to 77% for the accelerated system. The corresponding percentages after 6 years were 25% and 52%, respectively. After the ninth year, only 1% of the annual system ewes survived in comparison with 5% for the accelerated system. Unfortunately, reasons for culling were not recorded for each individual ewe and therefore, exact interpretation cannot be given. However, health disorder problems as a culling reason are excluded because all flocks with serious health problems were not included in this work. Lifetime averaged 1948 and 2351 days for annual and accelerated lambing systems, respectively. Conington et al. (2001) reported that longevity of Hill ewes in UK averaged 1756 days. This estimate cannot be compared directly with that for Churra ewes, however, due to differences in both the production pattern and the breeding objectives. Hill sheep are a grazing breed mainly used for meat production. The main goals of their breeding program are improving maternal performance and carcass and growth characteristics of lambs. Available literature does not provide information on lifetime traits of dairy ewes in annual and accelerated lambing systems. In the annual system, productive life accounted for 54% of total lifetime of the ewe while useful life represented 27% and 50% of lifetime and productive life, respectively. The corresponding figures for the accelerated system were 62%, 35% and 56%, respectively. Therefore, the percentages of productive life and useful life were higher in the accelerated system. Non-productive periods, the time from birth to first parturition and cumulative dry periods during lifetime, averaged 591 and 528 days, respectively, in the annual system. The corresponding figures for the accelerated system were 607 and 634 days, respectively. Although age at first lambing was significantly higher in the accelerated system (Table 2), it represented 26% of ewe lifetime in the accelerated system versus 30% in the annual system. Cumulative dry periods during lifetime represented 27% in both systems. The means for both non-productive periods are greater than desired from an economic point-of-view especially in the accelerated lambing system. Both measures are directly affected by the reproductive efficiency of the ewe. The average interval between successive lambings varied greatly among ewes in the accelerated
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system (from 202 to 558 days). This wide range could be attributed to differences in reproductive management between flocks and individual fertility differences among ewes. This variable was less than 8 months in only 14% of accelerated system ewes. Moreover, 30% of accelerated system ewes averaged more than 10 months. Fifty eight percent of ewes with more than 10 months had higher revenues than the overall mean of total revenues from milk and lambs during lifetime. Ewes with high milk yields tend to have a lower fertility (Robinson et al., 2002, in press). Therefore, management to improve reproductive performance is needed. Improving reproductive performance would help in increasing profitability of dairy sheep farms. The lower the non-productive periods, the lower the fixed maintenance cost of the animal. However, suitable dry periods are necessary as a biological and financial investment in the future profitability of the animal (Lormore and Galligan, 2001). Improved management practices are greatly needed to ensure both better fertility and suitable dry periods in the accelerated lambing system. Useful life averaged 523 and 820 days in the annual and accelerated lambing systems, respectively. These means correspond to an average of 138 and 144 days/ parity, respectively. These results are consistent with accepted management practices inasmuch as the average suckling period in Churra is 30 days, after which ewes are normally milked for approximately 120 days. The average lifetime milk yield in this study was 511 and 817 l for annual and accelerated systems, respectively, i.e. an average of 135 and 143 l per lactation, respectively. Previous studies on Churra breed (Carriedo et al., 1995; El-Saied et al., 1998, 1999) reported that standardized 120-day milk yield ranged between 102 and 133 l. Previous studies on Churra dairy ewes (Baro et al., 1994; El-Saied et al., 1998; Fuertes et al., 1998) found that daily milk yield ranged between 0.85 and 1.10 l. Estimate of milk/day of useful life from this study (0.91 and 0.96 for annual and accelerated systems, respectively) falls within that range. Milk/day of lifetime averaged 0.24 and 0.32 l for annual and accelerated systems, respectively. The corresponding figures for milk/day of productive life were 0.49 and 0.58, respectively. The average number of lambs sold at weaning during lifetime was 5.2 and 8.2, respectively, for annual
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and accelerated systems, i.e. an average of 1.4 weaned lambs/parity in both cases. Multiple birth lambing is a frequent event in dairy ewes that positively affects its final profit. Ewes that give birth to multiple lambs usually produce higher milk yield than single lambing ewes (El-Saied et al., 1999) mainly due to the hormonal effect of the placenta on the development of the udder during the gestation period. Weaned Churra lambs are typically consumed and highly valued in the region of Castilla-Leo´n, Spain. Total revenues from milk and lambs during the lifetime of Churra ewes averaged 583 and 936 Euro in annual and accelerated lambing systems, respectively. Averages for revenues/day for each of lifetime, productive life and useful life were 0.28, 0.58 and 1.08 Euro in the annual system and 0.37, 0.67 and 1.10 Euro, respectively, in the accelerated system. On average, lambs contributed 43% and 42% of total revenues during lifetime of the ewe in annual and accelerated systems, respectively. These results show that lamb production is economically important for Churra breeders. Therefore, attention should be given to both milk and lamb yields in future profitability and breeding studies for Churra dairy sheep. Tables 3 and 4 present statistical significance and percentage of variance explained by fixed effects for lifetime performance traits in annual and accelerated lambing systems. Flock contributed significantly to variations in all traits in both systems except for lifetime and revenues/day of productive life in the accelerated system. Average percentage of variance explained by flock was 14% and 12%, respectively, for annual and accelerated systems. In the annual system, the effect of birth year of the ewe had a significant effect on all variables except for milk/day of productive life, average interval between successive lambings and revenues/day of productive life. However, this effect was only significant on variation of age at first lambing and revenues/day of useful life of the accelerated system. Average variance explained by this effect in the annual system ranged from 0.3% to 10.3%. Season of birth of the ewe contributed significantly to variation of only two traits: lifetime and age at first lambing in the accelerated system and explained less than 1.1% of total variance in both systems. Therefore, it was decided to exclude this effect from the mixed animal model.
Table 4 Percentage of variance explained by flock (FL), ewe year of birth (YB), ewe season of birth (S), milk production level (PL) and the sum of variance explained by effects included in the model (Sum) on lifetime performance traits under annual (A) and accelerated (B) lambing systems Trait1
LT, day PL, day UL, day TMY, l M / dLT, l M / dPL, l M / dUL, l Age1L, d Lifetime score Interv Lambs TRLT R / dLT R / dPL R / dUL
FL
YB
S
PL
Sum
A
B
A
B
A
B
A
B
A
B
14.7 8.8 13.1 16.6 20.2 16.4 18.5 12.0 13.9 9.1 15.5 17.4 19.3 9.2 11.8
0.0 8.1 10.6 15.7 25.1 7.8 10.0 4.8 11.8 11.4 15.3 16.4 27.9 3.6 6.2
6.5 2.8 2.6 1.0 1.1 0.7 1.9 10.3 3.0 0.0 2.5 1.5 0.7 0.3 1.4
0.0 0.0 0.0 0.0 0.0 0.0 0.2 4.3 0.0 0.2 0.0 0.0 0.0 0.0 1.81
0.2 0.1 0.4 0.2 0.1 0.0 0.0 0.9 0.2 0.0 0.0 0.1 0.0 0.0 0.0
0.9 0.62 4.8 0.7 0.0 0.0 0.0 5.4 0.6 1.9 0.5 0.7 0.0 0.3 0.0
23.9 24.5 24.0 – – – – – 20.2 – – – – – –
6.7 7.2 9.8 – – – – – 7.6 – – – – – –
45.3 36.2 40.1 17.8 21.4 17.1 20.4 23.2 37.3 9.1 18.0 19.0 20.0 9.5 13.2
7.6 15.9 25.2 16.4 25.1 7.8 10.2 14.5 20.0 13.5 15.8 17.1 27.9 3.9 8.0
1
LT = Lifetime; PL = productive life; UL = useful life; TMY = total milk yield; M / dLT = milk per day of lifetime; M / dPL = milk per day of productive life; M / dUL = milk per day of useful life; Age1L = age at first lambing; Lifetime score = number of given parities during LT; Interv = average interval between successive lambings; Lambs = lambs sold at weaning during LT; TRLT = total revenue from milk and lambs during lifetime; R / dLT = revenue from milk and lambs/day of lifetime; R / dPL = revenue from milk and lambs/day of productive life; R / UL = revenue from milk and lambs/day of useful life.
Milk production level contributed significantly ( P b 0.001) to variations of all life span traits (lifetime, productive life, useful life and lifetime score) in both systems. Moreover, it explained a high percentage of variance for all life span traits. Percentage of variance explained by milk production level averaged 23% out of the 40% explained by the whole model for the annual system. The corresponding figures for the accelerated system were 8% out of 17%, respectively. These results demonstrated the great importance of milk production level for variation in life span traits. Table 5 presents least squares means of total life span traits by milk production level in both lambing systems. The relationship between production level and life span traits is clearly successive. All life span traits increased gradually with productive level. With respect to the overall mean; each of lifetime, productive life, useful life and lifetime score was
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Table 5 Least squares means of life span traits by milk production level1 within each of annual and accelerated lambing systems Trait2
LT, day PL, day UL, day Lifetime score
Annual system
Accelerated system
Level 1 (lowest)
Level 2
Level 3
Level 4
Level 5 (highest)
Level 1 (lowest)
Level 2
Level 3
Level 4
Level 5 (highest)
1526d 612d 333d 2.6d
1862c 908c 458c 3.4c
2159b 1201b 598b 4.2b
2371a 1410a 687a 4.8a
2431a 1428 a 696a 4.7a
2065b 944c 484c 3.7c
2246b 1200b 667b 4.8b
2487a 1452a 801a 5.7a
2497a 1465a 798a 5.6a
2569a 1477a 845a 5.9a
1
The five levels were determined in function of mean and SD of milk/day of useful life as, V 0.64, N0.64 to 0.78, N0.78 to 1.08, N1.08 to 1.22 and N1.22 l of milk/day of useful life, respectively. 2 LT = Lifetime; PL = productive life; UL = useful life; Lifetime score = number of given parities during LT. a, b, c, d: Means in a row with different superscript differ ( P b 0.05).
increased by 47%, 78%, 69% and 55%, respectively, between lowest and highest productive levels in the annual system. The corresponding figures for the accelerated system were 21%, 37%, 44% and 39%, respectively. Therefore, the effect of milk productive level should be included in genetic models for life span traits of dairy ewes to adjust these traits due to voluntary culling decisions. Tables 6 and 7 present heritabilities and phenotypic and genetic correlations among lifetime performance traits in annual and accelerated lambing systems, respectively. Detailed discussion on heritability and phenotypic and genetic correlations among lifetime traits and future possibilities for genetic improvement for Churra dairy ewes are available in the work of ElSaied et al. (2005). In this work, heritability estimates for productive and life span traits were clearly lower in the case of the accelerated system (0.02 to 0.20) compared with the annual system (0.08 to 0.45). Age at first lambing was the only trait that had a higher heritability estimate (0.13) in the accelerated lambing system compared with the annual lambing one (0.03). Similarly, both phenotypic and genetic correlations among lifetime performance traits were much higher in the case of the annual lambing system compared with the accelerated one. Due to the relatively poor reproductive performance of some ewes in the accelerated lambing system, failure to lamb three times in two consecutive years was most likely. The average interval between successive lambings was more than 10 months for 30% of the accelerated lambing system ewes and some of these ewes averaged more than 550 days. These ewes were kept probably due to their high level of milk yield. Therefore, the same flock included ewes
with considerable differences in their reproductive performance resulting in a non-homogeneous system within each flock. Non-pregnant ewes in the annual system had a lower number of insemination group opportunities/year compared with ewes in the accelerated system. Number of groups/year in the accelerated lambing system was not fixed but varied from flock to flock and from one year to another within flock depending on many factors including the strategy of each breeder and market demand of lambs. The number of these groups/year varied from 2 to 6. The higher the number of these opportunities/year, the better the possibility of achieving more pregnant ewes. Therefore, ewe output is expected to vary across flocks in the accelerated system. This means that the effect of reproductive intensity is not fixed for each flock but variable; practically for each ewe depending on its reproductive performance and the number of insemination group opportunities/year applied by each breeder. Under these conditions, it seems very difficult to design a suitable model to take into account these particular differences. This is supported by the lower percentage of variance explained for the majority of variables for the accelerated lambing system compared with the annual one (Table 4). The lower the variance explained, the higher the error of the model. These results would explain the differences in heritability and genetic correlation estimates for lifetime traits between both systems. Nugent and Jenkins (1992) stated that culling of ewes based on performance for scarcely repeatable traits such as fertility could be unfavourable to system productivity. The authors added that management to ensure high fertility, especially among young ewes, would be of more importance than removing non-
188
LT
PL
UL
TMY
M / dLT
M / dPL
M / dUL
Age1L
Lifetime score
Lambs
TRLT
R / dLT
LT 0.11 (0.05) 0.89 0.84 0.98 0.94 0.78 0.68 0.29 0.78 0.96 0.98 0.95 PL 0.91 0.16 (0.05) 0.99 0.99 0.98 0.68 0.65 0.16 0.99 0.97 0.99 0.98 UL 0.89 0.97 0.20 (0.06) 0.99 0.99 0.29 0.70 0.04 0.99 0.96 0.99 0.98 TMY 0.82 0.89 0.91 0.43 (0.07) 0.99 0.75 0.91 0.14 0.99 0.95 0.99 0.99 M / dLT 0.55 0.70 0.75 0.90 0.45 (0.08) 0.84 0.94 0.05 0.98 0.90 0.98 0.98 M / dPL 0.01 0.02 0.06 0.32 0.51 0.20 (0.06) 0.95 0.80 0.56 0.38 0.67 0.68 M / dUL 0.36 0.38 0.40 0.67 0.81 0.80 0.36 (0.08) 0.44 0.67 0.71 0.87 0.85 Age1L 0.15 0.07 0.08 0.11 0.27 0.07 0.10 0.03 (0.03) 0.02 0.20 0.20 0.12 Lifetime score 0.90 0.98 0.97 0.86 0.67 0.04 0.33 0.04 0.18 (0.05) 0.97 0.99 0.99 Lambs 0.83 0.91 0.90 0.83 0.67 0.01 0.36 0.01 0.92 0.15 (0.07) 0.97 0.96 TRLT 0.86 0.93 0.95 0.98 0.85 0.22 0.58 0.08 0.92 0.92 0.36 (0.07) 0.99 R / dLT 0.56 0.74 0.78 0.86 0.94 0.35 0.67 0.26 0.73 0.80 0.88 0.32 (0.08) R / dPL 0.17 0.20 0.12 0.10 0.26 0.87 0.55 0.02 0.20 0.05 0.06 0.22 R / dUL 0.29 0.30 0.28 0.52 0.61 0.59 0.80 0.02 0.28 0.46 0.52 0.64 1
R / dPL
R / dUL
0.98 0.47 0.99 0.41 0.90 0.47 0.56 0.86 0.66 088 0.82 0.68 0.76 0.90 0.48 0.27 0.99 0.49 0.17 0.67 0.47 0.84 0.51 0.85 0.08 (0.04) 0.72 0.62 0.17 (0.06)
SE for genetic correlations ranged from 0.01 to 0.43. 2LT = Lifetime; PL = productive life; UL = useful life; TMY = total milk yield; M / dLT = milk/day of lifetime; M / dPL = milk/day of productive life; M / dUL = milk/day of useful life; Age1L = age at first lambing; Lifetime score = number of given parities during LT; Interv = average interval between successive lambings; Lambs = lambs sold at weaning during LT; TRLT = total revenue from milk and lambs during lifetime; R / dLT = revenue from milk and lambs/day of lifetime; R / dPL = revenue from milk and lambs/day of productive life; R / dUL = revenue from milk and lambs/day of useful life.
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Table 6 Heritabilities F SE (on the diagonal), genetic correlations1 (above the diagonal) and phenotypic correlations (below the diagonal) among lifetime performance traits2 under the annual lambing system
LT
PL
UL
TMY
M / dLT
M / dPL
M / dUL
Age1L
Lifetime score
Lambs
TRLT
R / dLT
R / dPL
R / dUL
LT 0.02 (0.01) .39 .35 0.05 0.44 0.42 0.48 0.54 0.56 0.87 0.28 0.20 0.18 0.15 PL 0.90 0.04 (0.01) 0.95 0.70 0.50 0.03 0.19 0.45 0.91 0.84 0.93 0.81 0.28 0.21 UL 0.85 0.97 0.05 (0.01) 071 0.57 0.05 0.18 0.44 0.94 0.77 0.90 0.82 0.24 0.14 TMY 0.74 0.85 0.90 0.07 (0.03) 0.92 .72 0.77 0.43 0.71 0.20 0.97 0.94 0.39 0.46 M / dLT 0.48 0.66 0.74 0.91 0.16 (0.04) 0.82 0.86 0.41 0.41 0.27 0.85 0.97 0.45 0.53 M / dPL 0.18 0.14 0.02 0.29 0.46 0.16 (0.03) 0.96 0.06 0.05 0.22 0.55 0.71 0.89 0.79 M / dUL 0.17 0.21 0.25 0.58 0.73 0.81 0.20 (0.06) 0.08 0.18 0.33 0.66 0.85 0.79 0.86 Age1L 0.07 0.15 0.15 0.12 0.21 0.06 0.02 0.13 (0.03) 0.15 0.50 0.42 0.24 0.20 0.23 Lifetime score 0.86 0.97 0.99 0.88 0.71 0.06 0.23 0.14 0.03 (0.01) 0.87 0.94 0.71 0.02 0.35 Lambs 0.81 0.92 0.94 0.86 0.71 0.01 0.26 0.11 0.95 0.03 (0.01) 0.49 0.38 0.54 0.52 TRLT 0.80 0.91 0.95 0.97 0.86 0.17 0.46 0.12 0.94 0.94 0.05 (0.03) 0.91 0.27 0.43 R / dLT 0.53 0.74 0.82 0.90 0.95 0.32 0.58 0.23 0.79 0.84 0.91 0.11 (0.03) 0.28 0.44 0.09 0.14 0.27 0.86 0.58 0.11 0.12 0.01 0.10 0.23 0.06 (0.02) 0.89 R / dPL 0.25 0.21 R / dUL 0.19 0.23 0.25 0.52 0.61 0.68 0.84 0.08 0.25 0.38 0.49 0.60 0.72 0.11 (0.03) 1
SE for genetic correlations ranged from 0.01 to 0.41. 2LT = Lifetime; PL = productive life; UL = useful life; TMY= total milk yield; M / dLT = milk/day of lifetime; M / dPL = milk/day of productive life; M / dUL = milk/day of useful life; Age1L = age at first lambing; Lifetime score = number of given parities during LT; Interv = average interval between successive lambings; Lambs = lambs sold at weaning during LT; TRLT = total revenue from milk and lambs during lifetime; R / dLT = revenue from milk and lambs/day of lifetime; R / dPL = revenue from milk and lambs/day of productive life; R / dUL = revenue from milk and lambs/day of useful life.
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Table 7 Heritabilities F SE (on the diagonal), genetic correlations1 (above the diagonal) and phenotypic correlations (below the diagonal) among lifetime performance traits2 under the accelerated lambing system
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lambing ewes. This is also recommended for Churra ewes in order to obtain more homogenous reproductive characteristics. This would contribute to improve modelling of lifetime traits.
4. Conclusions Clear differences in phenotypic and genetic parameter estimates were observed for productivity and lifetime traits between annual and accelerated lambing systems. Due to the relatively low fertility, the means for non-productive periods were greater than desired from an economic point-of-view, especially for the accelerated lambing system. Therefore, management to improve reproductive performance is strongly recommended especially for the young high yielding ewes of flocks under the accelerated lambing system. This would contribute to obtaining more homogenous reproductive characteristics, improving modelling of lifetime traits and probably genetic parameters estimation, too. Potential opportunities for genetic improvement increase with better modelling.
References Allaire, F.R., Gibson, J.P., 1992. Genetic value of herd life adjusted for milk production. J. Dairy Sci. 75, 1349 – 1356. Baro, J.A., Carriedo, J.A., San Primitivo, F., 1994. Genetic parameters of test day measures for somatic cell count, milk yield, and protein percentage of milking ewes. J. Dairy Sci. 77, 2658 – 2662. Boettcher, P.J., Jairath, L.K., Koots, K.R., Dekkers, J.C.M., 1997. Effect of interactions between type and milk production on survival traits of Canadian Holsteins. J. Dairy Sci. 80, 2984 – 2995. Carriedo, J.A., Baro, J.A., de la Fuente, L.F., San Primitivo, F., 1995. Genetic parameters for milk yield in dairy sheep. J. Anim. Breed. Genet. 112, 59 – 63. Conington, J., Bishop, S.C., Grundy, B., Waterhouse, A., Simm, G., 2001. Multi-trait selection indexes for sustainable improvement of UK Hill sheep. Proceeding of the British Society of Animal Science. Annual Meeting. York, UK., 9th–11th April, 40. Dekkers, J.C.M., 1993. Theoretical basis for genetic parameters of herd life and effects on response to selection. J. Dairy Sci. 76, 1433 – 1443.
Dekkers, J.C.M., Jairath, L.K., Laurance, B.H., 1994. Relationships between sire genetic evaluation for conformation and functional herd life of daughters. J. Dairy Sci. 77, 844 – 854. El-Saied, U.M., Carriedo, J.A., San Primitivo, F., 1998. Heritability of test day somatic cell counts and its relationship with milk yield and protein percentage in dairy ewes. J. Dairy Sci. 81, 2956 – 2961. El-Saied, U.M., Carriedo, J.A., de la Fuente, L.F., San Primitivo, F., 1999. Genetic parameters of lactation cell counts and milk and protein yields in dairy ewes. J. Dairy Sci. 82, 639 – 644. El-Saied, U.M., de la Fuente,, Carriedo, J.A., San Primitivo, F., 2005. Genetic and phenotypic parameter estimates of total and partial lifetime traits for dairy ewes. J. Dairy Sci. 88, 3265 – 3272. Fuertes, J.A., Gonzalo, C., Carriedo, J.A., San Primitivo, F., 1998. Parameters of test day milk yield and milk components for dairy ewes. J. Dairy Sci. 81, 1300 – 1307. Gonzalo, C., Carriedo, J.A., Blanco, M.A., Beneitez, E., Juarez, M.T., de la Fuente, L.F., San Primitivo, F., 2005. Factors of variation influencing bulk tank somatic cell count in dairy sheep. J. Dairy Sci. 88, 969 – 974. Groeneveld, E., Garcı´a Corte´s, L.A., 1998. VCE 4.0, a (co)variance component package for frequentists and Bayesians. Proc. 6th. World Congress on Genetics Applied to Livestock Production, vol. 27, pp. 455 – 456. Jairath, L.K., Hayes, J.F., Cue, R.I., 1994. Multitrait restricted maximum likelihood estimates of genetic and phenotypic parameters of lifetime performance traits for Canadian Holsteins. J. Dairy Sci. 77, 303 – 312. Lormore, M.J., Galligan, D.T., 2001. Economics of a typical lactation. J. Dairy Sci. 84 (E. Suppl.), E212 – E215. Mulder, H., Jansen, G., 1999. Derivation of economic values using lifetime profitability of Canadian Holstein cows. Inter Bull. 21, 1 – 10. Nugent, R.A., Jenkins, T.G., 1992. Effect of alternative lamb production systems, maternal line, and culling strategy on flock age structure. J. Anim. Sci. 70, 2285 – 2295. Othmane, M.H., de la Fuente, L.F., Carriedo, J.A., San Primitivo, F., 2002. Heritability and genetic correlations of test day milk yield and composition, individual laboratory cheese yield, and somatic cell count for dairy ewes. J. Dairy Sci. 85, 2692 – 2698. Pe´rez-Cabal, M.A., Alenda, R., 2003. Lifetime profit as an individual trait and prediction of its breeding values in Spanish Holstein cows. J. Dairy Sci. 86, 4115 – 4122. Robinson, J.J., Ashworth, C.J., Rooke, J.A., L.M.,, McEvoy, T.G., 2002. Nutrition for conception and pregnancy. In: Freer, M., Dove, H. (Eds.), Sheep Nutrition. CAB International, Wallingford, UK, pp. 189 – 211. Robinson, J.J., Ashworth, C.J., Rooke, J.A., Mitchell, L.M., McEvoy, T.G., in press. Nutrition and fertility in ruminant livestock. Animal Feed Science and Technology. Available online 19 September 2005. SAS User’s Guide, Statistics, Release 6.12. 1998. SAS Inst., Inc., Cary, NC.
Lifetime traits comparison between annual and accelerated lambing systems for dairy ewes U.M. El-Saied a,*, L.F. de la Fuente b, F. San Primitivo b b
a Animal Production Research Institute, Nadi El-Said St., Dokki, Giza, Egypt Departamento de Produccio´n Animal I, Facultad de Veterinaria, Universidad de Leo´n, 24071 Leo´n, Spain
Received 2 June 2005; received in revised form 18 October 2005; accepted 1 November 2005
Abstract Two sets of data with a sum of 6318 lactations for 1391 Spanish Churra ewes, belonging to 10 flocks were used to study phenotypic, genetic and system efficiency parameters of lifetime traits in annual and accelerated lambing systems. The study included four life span traits, three productive traits and two reproductive traits. Trait averages for both milk yield and revenues from sold milk and weaned lambs were calculated per-day of lifetime, productive life and useful life. The animal model included flock and ewe birth year as fixed effects. Both effects contributed significantly to variation in most traits in the annual system while birth year was non-significant for most variables of the accelerated system. Milk production level was included in the model to analyze life span traits. It contributed significantly to variation in all life span traits in both systems. Means for productive and life span traits were significantly higher in the accelerated system compared with the annual system. The average interval between successive lambings was significantly shorter in the accelerated system, while age at first lambing was significantly lower in the annual system. Except for age at first lambing, heritability estimates were clearly lower in the case of the accelerated system (0.02 to 0.20) than in the annual system (0.08 to 0.45). Genetic correlations among traits were also lower in the case of the accelerated system. Failure to lamb three times in two consecutive years and the varying reproductive management among flocks in the accelerated system may be responsible for the differences in genetic results between the two systems. Improving reproductive performance is necessary, especially for the young high yielding ewes in the accelerated system. Management to ensure high fertility, especially among young ewes, would be of more importance than removing nonlambing ewes. D 2005 Elsevier B.V. All rights reserved. Keywords: Genetic parameters; Lifetime traits; Lambing systems; Dairy ewes
1. Introduction * Corresponding author. Present mailing address: Departamento de Produccio´n Animal I, Facultad de Veterinaria, Universidad de Leo´n, 24071 Leo´n, Spain. Tel.: +34 987 29 12 88; fax: +34 987 29 13 11. E-mail address: [email protected] (U.M. El-Saied). 0301-6226/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2005.11.003
As is the case for numerous dairy breeds in several countries, genetic selection in Churra dairy ewes has placed primary emphasis on milk yield for many years.
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In the last 5 years, however, there has been increased interest for selecting additional traits to increase profitability including protein percentage and udder and type traits. Longevity, or length of lifetime, is a composite trait of production, health and reproduction (Mulder and Jansen, 1999). Long lifetime indicates good health and fertility, allows the animal to achieve its maximum productive capacity, contributes to reducing replacement and treatment costs, means fewer losses due to involuntary culling and increases the scope of voluntary culling (Dekkers, 1993; Jairath et al., 1994; Boettcher et al., 1997). Because of its effect on economic performance, lifetime has been seen as a trait of interest for animal breeders, in general, and dairy breeders in particular (Allaire and Gibson, 1992; Dekkers et al., 1994; Pe´rez-Cabal and Alenda, 2003). Profit maximization on dairies is dependent on the ability of the herd management program to maximally reduce the acquisition and maintenance cost of animals throughout their lives (Lormore and Galligan, 2001). The annual lambing system is very common in ovine breeds. However, Churra dairy sheep breeders apply either the classic annual lambing system or the accelerated system of lambing three times in 2 years. Therefore, life span traits (productive life, useful life and lifetime score) and yields of milk and lambs during the lifetime of the ewe and consequently the final profit are expected to vary from one system to another. The objective of this work was to compare estimates for phenotypic and genetic parameters and some efficiency parameters of various lifetime traits in Churra dairy ewes according to the lambing system (annual or accelerated), discuss both the possible
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reasons behind the expected differences and future possibilities of improvement.
2. Materials and methods 2.1. Data Data were obtained from the National Association of Spanish Churra Breeders (ANCHE, Palencia, Spain) and were collected between 1990 and 2003. Table 1 presents a summary of the data analysed in this work. Two sets of data were considered. The first set considered six flocks applying an annual lambing system while the second contained four flocks applying an accelerated system to lamb three times in 2 years. In both sets of data, records included dates of birth, lambing, dry off and culling and yields for milk and lambs. All flocks were enrolled in the nucleus scheme of the Spanish Churra dairy breed. Late gestation ewes are usually kept together in a single yard; many of them give birth to multiple lambs. In order to prevent wrong dam-lamb assignation, pedigree control is regularly done by the Department of Animal Production I, University of Leo´n (Leo´n, Spain) using DNA genetic markers on sample individuals from all those flocks enrolled in the nucleus scheme of Churra breed. All ewes were daughters of AI sires and were artificially inseminated themselves; therefore, complete pedigree information was available over the study. Many genetic links existed among the flocks due to extensive use of AI. There were management similarities between annual and accelerated lambing systems. In both systems, ewes were permanently
Table 1 Description of data for lifetime performance traits under annual and accelerated lambing systems Item
Annual system
Accelerated system
Ewes with records, no. Lactations, no. Sires, no. Daughters/sire, range Flocks, no. Connected flocks by each sire, range Dams, no. Dams with records, no. Parities/ewe, range Years of birth of the ewe
838 3150 63 1–81 6 2–6 691 84 1–10 1990 to 1995, inclusive
553 3168 65 1–55 4 2–4 464 39 1–14 1990 to 1995, inclusive
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housed indoors at night and grazed during the day under stable management and nutritional conditions. Lambing usually took place during autumn (39% in annual system and 45% in the accelerated one) and spring (38% in annual system and 41% in the accelerated one) and flock size is around 400 ewes. More details on management of Churra flocks were previously reported (Gonzalo et al., 2005). In both systems, the suckling period averaged 30 days and ewes were milked for approximately 120 day after weaning. Lambs were typically slaughtered after weaning to meet the market demand. Milk yield per lactation was estimated by ANCHE using a set of test-day records taken at monthly intervals following an alternative a.m.–p.m. recording scheme. Fat and protein in milk were measured by the automated infrared absorption spectrophotometry method (Milk-o-Scan; Foss Electric, Hillerød, Denmark) by the analysis service of the milk-testing program for the local government. According to the testing program applied for Spanish ewes in both annual and accelerated lambing systems, the first test day record was obtained at least 3 days following weaning, between the 31st and 75th day postpartum, and at approximately monthly intervals thereafter. The interval between lambing and first test day averaged 45.69 and 45.99 days in annual and accelerated systems, respectively. Details on yield recording of Churra ewes have been reported by El-Saied et al. (1998, 1999). All ewes had to have consecutive lactations, starting with the first. Ewes were born between 1990 and 1995 and therefore the youngest ewes had at least 9 years of opportunity of life. Lambing took place between 1992 and 2003, inclusive. Ewes were kept in the same flock throughout their lives. An age at first lambing of between 12 and 36 months was required and the lambing interval was restricted to between 180 and 599 days. The end of data recording was due to mortality, accidents, health disorders or low production. Unfortunately, reasons for culling were not recorded for each individual ewe. For modelling purposes, all ewes had to remain in the same flock throughout their lives. 2.2. Traits The present study included two productive traits: total milk yield during lifetime and number of lambs
sold at weaning during the lifetime of each ewe. Ewe lifetime productivity from both milk and lambs were transformed into their equivalent sum of revenues according to their prices. The milk and lamb pricing system did not change during the time of data recording. Lambs were always sold after weaning (3 to 4 weeks of age) to be slaughtered at 10–15 kg of live body weight. Churra milk is exclusively made into cheese. Therefore, milk composition in protein and fat was the determining factor of yield and quality of the final product and consequently of milk price. Detailed information on this aspect is available in the work of Othmane et al. (2002). In the present study, revenues from milk were calculated as a function of milk yield and, protein and fat content. There were no differences in milk pricing system between the two lambing systems. Average prices were 6.3 Eurocent/l of milk and 48 Euro/lamb at weaning. Both Churra cheese and Churra lambs have a Denomination of Origin in the region of Castilla-Leo´n, Spain. Reproductive performance traits included: 1) age at lambing and 2) average interval among consecutive lactations during lifetime of each ewe. Literature presents various measures for life span. Due to the lack of research work on lifetime performance for dairy ewes, it was decided to evaluate several lifetime performance traits to completely describe ewe lifetime. Thus, complete observations were required and this is only possible for ewes with recorded culling dates (i.e. no censored records were present). The study considered 4 variables related to the life of the ewe including: 1) total lifetime (number of days between birth and culling), 2) productive life (length of time between first lambing and the last dry date), 3) useful life (total number of days in milk (DIM) during lifetime) and 4) lifetime score, i.e. the number of lactations a ewe survived. Dekkers (1993) mentioned that length of productive life is a trait of major economic importance as it combines productive and reproductive aspects excluding age at first parity. Two intervals of time that are unprofitable from a milk production standpoint are the period from birth to first parturition and dry periods (Lormore and Galligan, 2001). These periods represent non-productive days that reduce profit of production per day of life. For that reason, other measures for life span were
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added that considered both productivity and life span. These measures included: 1) milk/day for each of lifetime, productive life and useful life; and 2) revenues from milk and lambs/day for lifetime, productive life and useful life. 2.3. Statistical analysis Genetic parameters were estimated within each set using REML and the VCE 4.0 software (Groeneveld and Garcı´a Corte´s, 1998) with the following multipletrait animal model: Yijkl ¼ Fi þ Y Bj þ Ak þ eijkl where: Yijkl = Productive and reproductive lifetime traits (for complete definition of all traits, please Table 2 Least squares means and standard errors (SE) of lifetime performance traits by lambing system effect Trait1
LT, day PL, day UL, day TMY, l M / dLT, l M / dPL, l M / dUL, l Age1L, d Lifetime score Interv2 Lambs TRLT, Euro R / dLT, Euro R / dPL, Euro R / dUL, Euro
Annual system
Accelerated system
Mean
Mean
b
2069 1099b 553b 582b 0.25a 0.51a 0.95a 615b 3.9b 330a 5.7b 652b 0.29b 0.58b 1.07a
SE 33 32 16 20 0.01 0.01 0.10 7 0.1 2 0.2 21 0.01 0.01 0.01
a
2354 1316a 721a 674a 0.27a 0.53a 0.90b 652a 5.1a 294b 7.3a 789a 0.32a 0.63a 1.09a
SE 44 43 21 27 0.01 0.01 0.01 10 0.1 3.1 0.3 28 0.01 0.01 0.01
1 LT = Lifetime; PL = productive life; UL = useful life; TMY = total milk yield; M / dLT = milk/day of lifetime; M / dPL = milk/day of productive life; M / dUL = milk/day of useful life; Age1L = age at first lambing; Lifetime score = number of given parities during lifetime; Interv = average interval between successive lambings; Lambs = lambs sold at weaning during LT; TRLT = total revenues from milk and lambs during lifetime; R / dLT = revenue from milk and lambs/day of lifetime; R / dPL = revenue from milk and lambs/ day of productive life; R / dUL = revenue from milk and lambs/day of useful life. 2 Number of analyzed records for average interval between successive lambings was 801 and 523 for first and second files, respectively. a, b: Means in a row with different superscript differ ( P b 0.05).
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refer to Table 2); F i = Fixed effect of flock i (6 levels in the annual system data and 4 levels in the accelerated system data); YBj = Fixed effect of year of birth j (6 levels in both cases); A k = Random additive genetic effect of individual k; e ijkl = Random residual effect. The model described above was a linear model. In theory, survival analysis is a more proper statistical method for analysis of lifetime traits because it deals properly with the typically skewed distributions of the data and can account for censored records. However, the use of the linear model was justifiable in this work. First, only uncensored ewes were used. Second, previous results for dairy cows (Jairath et al., 1994) indicated that REML estimates from a linear model can be of practical use even when normality does not hold. Genetic selection in Churra dairy ewes has placed primary emphasis on milk production for many years. Therefore, life span traits are expected to be largely affected by milk production level. In this work, milk/day of useful life was added to the abovementioned model as a fixed effect with five levels to analyse life span traits (lifetime, productive life, useful life and lifetime score). The five levels were determined as a function of mean and SD of milk/day of useful life as: V 0.64, N0.64 to 0.78, N 0.78 to 1.08, N1.08 to 1.22 and N 1.22 l of milk/day of useful life, respectively. Each year was divided into four seasons: January through March, April through June, July through September and October through December. The results demonstrated non-significant effect of season of birth of the ewe on all traits (Table 3). Therefore, season effect was excluded from the mixed animal model. All known relationships among individuals were considered in the animal model. Phenotypic parameters were estimated by GLM and VARCOMP procedures of SAS (SAS, 1998).
3. Results and discussion We combined in a first analysis data from both systems where lambing system was added as a fixed effect to the phenotypic model in order to compare least squares means for lifetime performance traits in annual and accelerated lambing systems. The results are given in Table 2.
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Table 3 F value and significance by lambing system (RS), flock (FL), ewe year of birth (YB), ewe season of birth (S) and milk production level (PL) on lifetime performance traits under annual and accelerated lambing systems Trait2
F value and significance1 Annual system
LT, day PL, day UL, day TMY, l M / dLT, l M / dPL, l M / dUL, l Age1L, d Lifetime score Interv Lambs TRLT R / dLT R / dPL R / dUL
Accelerated system
FL
YB
S
PL
FL
YB
S
PL
16.47*** 10.72*** 15.26*** 18.05*** 28.07*** 28.19*** 27.27*** 21.80*** 16.99*** 9.53*** 12.15*** 16.54*** 22.78*** 16.89*** 13.15***
12.65*** 5.79*** 5.62*** 2.95* 3.06*** 1.90NS 4.15*** 12.42*** 6.38*** 0.65NS 4.65*** 3.65*** 2.35* 1.65NS 2.82*
1.61NS 1.41NS 1.68NS 1.54NS 1.39NS 0.37NS 0.42NS 2.03NS 1.39NS 0.65NS 0.71NS 1.29NS 0.86NS 0.57NS 0.26NS
46.70*** 41.50*** 43.11*** – – – – – 35.15*** – – – – – –
1.10NS 11.19*** 17.09*** 20.86*** 33.56*** 3.18* 5.26*** 4.43*** 17.62*** 14.06*** 22.55*** 22.62*** 42.38*** 2.39NS 4.58***
1.61NS 1.00NS 0.95NS 1.36NS 0.80NS 0.35NS 1.48NS 3.86*** 1.12NS 0.97NS 1.57NS 1.31NS 1.06NS 0.64NS 2.65*
3.15* 2.03NS 1.62NS 2.23NS 0.51NS 0.78NS 0.68NS 8.08*** 1.93NS 1.88NS 1.87NS 2.15NS 0.34NS 1.44NS 0.70NS
5.62*** 7.17*** 9.73*** – – – – – 7.83*** – – – – – –
1
*** = significant at P b 0.001, * = significant at P b 0.05, NS = non-significant. LT = Lifetime; PL = productive life; UL = useful life; TMY = total milk yield; M / dLT = milk per day of lifetime; M / dPL = milk per day of productive life; M / dUL = milk per day of useful life; Age1L = age at first lambing; Lifetime score = number of given parities during LT; Interv = average interval between successive lambings; Lambs = lambs sold at weaning during LT; TRLT = total revenue from milk and lambs during lifetime; R / dLT = revenue from milk and lambs/day of lifetime; R / dPL = revenue from milk and lambs/day of productive life; R / UL = revenue from milk and lambs/day of useful life.
2
tended to keep milking them until they got pregnant resulting in a significantly longer useful life and consequently a significantly lower milk/day of useful life compared with annual lambing system ewes. Fig. 1 shows survival curves for Churra ewes in annual and accelerated lambing systems along with age of ewes. A better survival rate was expected in the annual lambing system due to the stress of frequent lambing on ewes in the accelerated system. However, Survival percentage
As expected, all life span traits (lifetime, productive life, useful life and lifetime score) were significantly higher in the accelerated system than in the annual one. Percent increase in these traits averaged 20% (ranging from 12% for total lifetime to 23.5% for lifetime score). Also, total milk yield produced during ewe lifetime, lambs sold at weaning during ewe lifetime, and milk and revenues/day for both lifetime and productive life were significantly higher in the accelerated system. As also expected, the average interval between successive lambings was significantly shorter in the accelerated lambing system. However, age at first lambing was significantly lower in the annual lambing system. Milk/day of useful life was significantly higher in the annual system and revenues from milk and lambs did not differ significantly between the two systems. Due to the negative relationship between high milk yield and reproductive performance (Robinson et al., 2002, in press), some higher yielding ewes in the accelerated system failed to get pregnant at the right time according to the accelerated system point-of-view. Therefore, breeders
100 80 60 40 20 0
2
3
4
5 6 Age (years)
Annual System
7
8
9
Accelerated system
Fig. 1. Survival curves for Churra ewes in annual and accelerated lambing systems along with age of ewes.
U.M. El-Saied et al. / Livestock Science 101 (2006) 180–190
the results showed that only 63% of the annual system ewes survived to the fourth year of age compared to 77% for the accelerated system. The corresponding percentages after 6 years were 25% and 52%, respectively. After the ninth year, only 1% of the annual system ewes survived in comparison with 5% for the accelerated system. Unfortunately, reasons for culling were not recorded for each individual ewe and therefore, exact interpretation cannot be given. However, health disorder problems as a culling reason are excluded because all flocks with serious health problems were not included in this work. Lifetime averaged 1948 and 2351 days for annual and accelerated lambing systems, respectively. Conington et al. (2001) reported that longevity of Hill ewes in UK averaged 1756 days. This estimate cannot be compared directly with that for Churra ewes, however, due to differences in both the production pattern and the breeding objectives. Hill sheep are a grazing breed mainly used for meat production. The main goals of their breeding program are improving maternal performance and carcass and growth characteristics of lambs. Available literature does not provide information on lifetime traits of dairy ewes in annual and accelerated lambing systems. In the annual system, productive life accounted for 54% of total lifetime of the ewe while useful life represented 27% and 50% of lifetime and productive life, respectively. The corresponding figures for the accelerated system were 62%, 35% and 56%, respectively. Therefore, the percentages of productive life and useful life were higher in the accelerated system. Non-productive periods, the time from birth to first parturition and cumulative dry periods during lifetime, averaged 591 and 528 days, respectively, in the annual system. The corresponding figures for the accelerated system were 607 and 634 days, respectively. Although age at first lambing was significantly higher in the accelerated system (Table 2), it represented 26% of ewe lifetime in the accelerated system versus 30% in the annual system. Cumulative dry periods during lifetime represented 27% in both systems. The means for both non-productive periods are greater than desired from an economic point-of-view especially in the accelerated lambing system. Both measures are directly affected by the reproductive efficiency of the ewe. The average interval between successive lambings varied greatly among ewes in the accelerated
185
system (from 202 to 558 days). This wide range could be attributed to differences in reproductive management between flocks and individual fertility differences among ewes. This variable was less than 8 months in only 14% of accelerated system ewes. Moreover, 30% of accelerated system ewes averaged more than 10 months. Fifty eight percent of ewes with more than 10 months had higher revenues than the overall mean of total revenues from milk and lambs during lifetime. Ewes with high milk yields tend to have a lower fertility (Robinson et al., 2002, in press). Therefore, management to improve reproductive performance is needed. Improving reproductive performance would help in increasing profitability of dairy sheep farms. The lower the non-productive periods, the lower the fixed maintenance cost of the animal. However, suitable dry periods are necessary as a biological and financial investment in the future profitability of the animal (Lormore and Galligan, 2001). Improved management practices are greatly needed to ensure both better fertility and suitable dry periods in the accelerated lambing system. Useful life averaged 523 and 820 days in the annual and accelerated lambing systems, respectively. These means correspond to an average of 138 and 144 days/ parity, respectively. These results are consistent with accepted management practices inasmuch as the average suckling period in Churra is 30 days, after which ewes are normally milked for approximately 120 days. The average lifetime milk yield in this study was 511 and 817 l for annual and accelerated systems, respectively, i.e. an average of 135 and 143 l per lactation, respectively. Previous studies on Churra breed (Carriedo et al., 1995; El-Saied et al., 1998, 1999) reported that standardized 120-day milk yield ranged between 102 and 133 l. Previous studies on Churra dairy ewes (Baro et al., 1994; El-Saied et al., 1998; Fuertes et al., 1998) found that daily milk yield ranged between 0.85 and 1.10 l. Estimate of milk/day of useful life from this study (0.91 and 0.96 for annual and accelerated systems, respectively) falls within that range. Milk/day of lifetime averaged 0.24 and 0.32 l for annual and accelerated systems, respectively. The corresponding figures for milk/day of productive life were 0.49 and 0.58, respectively. The average number of lambs sold at weaning during lifetime was 5.2 and 8.2, respectively, for annual
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and accelerated systems, i.e. an average of 1.4 weaned lambs/parity in both cases. Multiple birth lambing is a frequent event in dairy ewes that positively affects its final profit. Ewes that give birth to multiple lambs usually produce higher milk yield than single lambing ewes (El-Saied et al., 1999) mainly due to the hormonal effect of the placenta on the development of the udder during the gestation period. Weaned Churra lambs are typically consumed and highly valued in the region of Castilla-Leo´n, Spain. Total revenues from milk and lambs during the lifetime of Churra ewes averaged 583 and 936 Euro in annual and accelerated lambing systems, respectively. Averages for revenues/day for each of lifetime, productive life and useful life were 0.28, 0.58 and 1.08 Euro in the annual system and 0.37, 0.67 and 1.10 Euro, respectively, in the accelerated system. On average, lambs contributed 43% and 42% of total revenues during lifetime of the ewe in annual and accelerated systems, respectively. These results show that lamb production is economically important for Churra breeders. Therefore, attention should be given to both milk and lamb yields in future profitability and breeding studies for Churra dairy sheep. Tables 3 and 4 present statistical significance and percentage of variance explained by fixed effects for lifetime performance traits in annual and accelerated lambing systems. Flock contributed significantly to variations in all traits in both systems except for lifetime and revenues/day of productive life in the accelerated system. Average percentage of variance explained by flock was 14% and 12%, respectively, for annual and accelerated systems. In the annual system, the effect of birth year of the ewe had a significant effect on all variables except for milk/day of productive life, average interval between successive lambings and revenues/day of productive life. However, this effect was only significant on variation of age at first lambing and revenues/day of useful life of the accelerated system. Average variance explained by this effect in the annual system ranged from 0.3% to 10.3%. Season of birth of the ewe contributed significantly to variation of only two traits: lifetime and age at first lambing in the accelerated system and explained less than 1.1% of total variance in both systems. Therefore, it was decided to exclude this effect from the mixed animal model.
Table 4 Percentage of variance explained by flock (FL), ewe year of birth (YB), ewe season of birth (S), milk production level (PL) and the sum of variance explained by effects included in the model (Sum) on lifetime performance traits under annual (A) and accelerated (B) lambing systems Trait1
LT, day PL, day UL, day TMY, l M / dLT, l M / dPL, l M / dUL, l Age1L, d Lifetime score Interv Lambs TRLT R / dLT R / dPL R / dUL
FL
YB
S
PL
Sum
A
B
A
B
A
B
A
B
A
B
14.7 8.8 13.1 16.6 20.2 16.4 18.5 12.0 13.9 9.1 15.5 17.4 19.3 9.2 11.8
0.0 8.1 10.6 15.7 25.1 7.8 10.0 4.8 11.8 11.4 15.3 16.4 27.9 3.6 6.2
6.5 2.8 2.6 1.0 1.1 0.7 1.9 10.3 3.0 0.0 2.5 1.5 0.7 0.3 1.4
0.0 0.0 0.0 0.0 0.0 0.0 0.2 4.3 0.0 0.2 0.0 0.0 0.0 0.0 1.81
0.2 0.1 0.4 0.2 0.1 0.0 0.0 0.9 0.2 0.0 0.0 0.1 0.0 0.0 0.0
0.9 0.62 4.8 0.7 0.0 0.0 0.0 5.4 0.6 1.9 0.5 0.7 0.0 0.3 0.0
23.9 24.5 24.0 – – – – – 20.2 – – – – – –
6.7 7.2 9.8 – – – – – 7.6 – – – – – –
45.3 36.2 40.1 17.8 21.4 17.1 20.4 23.2 37.3 9.1 18.0 19.0 20.0 9.5 13.2
7.6 15.9 25.2 16.4 25.1 7.8 10.2 14.5 20.0 13.5 15.8 17.1 27.9 3.9 8.0
1
LT = Lifetime; PL = productive life; UL = useful life; TMY = total milk yield; M / dLT = milk per day of lifetime; M / dPL = milk per day of productive life; M / dUL = milk per day of useful life; Age1L = age at first lambing; Lifetime score = number of given parities during LT; Interv = average interval between successive lambings; Lambs = lambs sold at weaning during LT; TRLT = total revenue from milk and lambs during lifetime; R / dLT = revenue from milk and lambs/day of lifetime; R / dPL = revenue from milk and lambs/day of productive life; R / UL = revenue from milk and lambs/day of useful life.
Milk production level contributed significantly ( P b 0.001) to variations of all life span traits (lifetime, productive life, useful life and lifetime score) in both systems. Moreover, it explained a high percentage of variance for all life span traits. Percentage of variance explained by milk production level averaged 23% out of the 40% explained by the whole model for the annual system. The corresponding figures for the accelerated system were 8% out of 17%, respectively. These results demonstrated the great importance of milk production level for variation in life span traits. Table 5 presents least squares means of total life span traits by milk production level in both lambing systems. The relationship between production level and life span traits is clearly successive. All life span traits increased gradually with productive level. With respect to the overall mean; each of lifetime, productive life, useful life and lifetime score was
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Table 5 Least squares means of life span traits by milk production level1 within each of annual and accelerated lambing systems Trait2
LT, day PL, day UL, day Lifetime score
Annual system
Accelerated system
Level 1 (lowest)
Level 2
Level 3
Level 4
Level 5 (highest)
Level 1 (lowest)
Level 2
Level 3
Level 4
Level 5 (highest)
1526d 612d 333d 2.6d
1862c 908c 458c 3.4c
2159b 1201b 598b 4.2b
2371a 1410a 687a 4.8a
2431a 1428 a 696a 4.7a
2065b 944c 484c 3.7c
2246b 1200b 667b 4.8b
2487a 1452a 801a 5.7a
2497a 1465a 798a 5.6a
2569a 1477a 845a 5.9a
1
The five levels were determined in function of mean and SD of milk/day of useful life as, V 0.64, N0.64 to 0.78, N0.78 to 1.08, N1.08 to 1.22 and N1.22 l of milk/day of useful life, respectively. 2 LT = Lifetime; PL = productive life; UL = useful life; Lifetime score = number of given parities during LT. a, b, c, d: Means in a row with different superscript differ ( P b 0.05).
increased by 47%, 78%, 69% and 55%, respectively, between lowest and highest productive levels in the annual system. The corresponding figures for the accelerated system were 21%, 37%, 44% and 39%, respectively. Therefore, the effect of milk productive level should be included in genetic models for life span traits of dairy ewes to adjust these traits due to voluntary culling decisions. Tables 6 and 7 present heritabilities and phenotypic and genetic correlations among lifetime performance traits in annual and accelerated lambing systems, respectively. Detailed discussion on heritability and phenotypic and genetic correlations among lifetime traits and future possibilities for genetic improvement for Churra dairy ewes are available in the work of ElSaied et al. (2005). In this work, heritability estimates for productive and life span traits were clearly lower in the case of the accelerated system (0.02 to 0.20) compared with the annual system (0.08 to 0.45). Age at first lambing was the only trait that had a higher heritability estimate (0.13) in the accelerated lambing system compared with the annual lambing one (0.03). Similarly, both phenotypic and genetic correlations among lifetime performance traits were much higher in the case of the annual lambing system compared with the accelerated one. Due to the relatively poor reproductive performance of some ewes in the accelerated lambing system, failure to lamb three times in two consecutive years was most likely. The average interval between successive lambings was more than 10 months for 30% of the accelerated lambing system ewes and some of these ewes averaged more than 550 days. These ewes were kept probably due to their high level of milk yield. Therefore, the same flock included ewes
with considerable differences in their reproductive performance resulting in a non-homogeneous system within each flock. Non-pregnant ewes in the annual system had a lower number of insemination group opportunities/year compared with ewes in the accelerated system. Number of groups/year in the accelerated lambing system was not fixed but varied from flock to flock and from one year to another within flock depending on many factors including the strategy of each breeder and market demand of lambs. The number of these groups/year varied from 2 to 6. The higher the number of these opportunities/year, the better the possibility of achieving more pregnant ewes. Therefore, ewe output is expected to vary across flocks in the accelerated system. This means that the effect of reproductive intensity is not fixed for each flock but variable; practically for each ewe depending on its reproductive performance and the number of insemination group opportunities/year applied by each breeder. Under these conditions, it seems very difficult to design a suitable model to take into account these particular differences. This is supported by the lower percentage of variance explained for the majority of variables for the accelerated lambing system compared with the annual one (Table 4). The lower the variance explained, the higher the error of the model. These results would explain the differences in heritability and genetic correlation estimates for lifetime traits between both systems. Nugent and Jenkins (1992) stated that culling of ewes based on performance for scarcely repeatable traits such as fertility could be unfavourable to system productivity. The authors added that management to ensure high fertility, especially among young ewes, would be of more importance than removing non-
188
LT
PL
UL
TMY
M / dLT
M / dPL
M / dUL
Age1L
Lifetime score
Lambs
TRLT
R / dLT
LT 0.11 (0.05) 0.89 0.84 0.98 0.94 0.78 0.68 0.29 0.78 0.96 0.98 0.95 PL 0.91 0.16 (0.05) 0.99 0.99 0.98 0.68 0.65 0.16 0.99 0.97 0.99 0.98 UL 0.89 0.97 0.20 (0.06) 0.99 0.99 0.29 0.70 0.04 0.99 0.96 0.99 0.98 TMY 0.82 0.89 0.91 0.43 (0.07) 0.99 0.75 0.91 0.14 0.99 0.95 0.99 0.99 M / dLT 0.55 0.70 0.75 0.90 0.45 (0.08) 0.84 0.94 0.05 0.98 0.90 0.98 0.98 M / dPL 0.01 0.02 0.06 0.32 0.51 0.20 (0.06) 0.95 0.80 0.56 0.38 0.67 0.68 M / dUL 0.36 0.38 0.40 0.67 0.81 0.80 0.36 (0.08) 0.44 0.67 0.71 0.87 0.85 Age1L 0.15 0.07 0.08 0.11 0.27 0.07 0.10 0.03 (0.03) 0.02 0.20 0.20 0.12 Lifetime score 0.90 0.98 0.97 0.86 0.67 0.04 0.33 0.04 0.18 (0.05) 0.97 0.99 0.99 Lambs 0.83 0.91 0.90 0.83 0.67 0.01 0.36 0.01 0.92 0.15 (0.07) 0.97 0.96 TRLT 0.86 0.93 0.95 0.98 0.85 0.22 0.58 0.08 0.92 0.92 0.36 (0.07) 0.99 R / dLT 0.56 0.74 0.78 0.86 0.94 0.35 0.67 0.26 0.73 0.80 0.88 0.32 (0.08) R / dPL 0.17 0.20 0.12 0.10 0.26 0.87 0.55 0.02 0.20 0.05 0.06 0.22 R / dUL 0.29 0.30 0.28 0.52 0.61 0.59 0.80 0.02 0.28 0.46 0.52 0.64 1
R / dPL
R / dUL
0.98 0.47 0.99 0.41 0.90 0.47 0.56 0.86 0.66 088 0.82 0.68 0.76 0.90 0.48 0.27 0.99 0.49 0.17 0.67 0.47 0.84 0.51 0.85 0.08 (0.04) 0.72 0.62 0.17 (0.06)
SE for genetic correlations ranged from 0.01 to 0.43. 2LT = Lifetime; PL = productive life; UL = useful life; TMY = total milk yield; M / dLT = milk/day of lifetime; M / dPL = milk/day of productive life; M / dUL = milk/day of useful life; Age1L = age at first lambing; Lifetime score = number of given parities during LT; Interv = average interval between successive lambings; Lambs = lambs sold at weaning during LT; TRLT = total revenue from milk and lambs during lifetime; R / dLT = revenue from milk and lambs/day of lifetime; R / dPL = revenue from milk and lambs/day of productive life; R / dUL = revenue from milk and lambs/day of useful life.
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Table 6 Heritabilities F SE (on the diagonal), genetic correlations1 (above the diagonal) and phenotypic correlations (below the diagonal) among lifetime performance traits2 under the annual lambing system
LT
PL
UL
TMY
M / dLT
M / dPL
M / dUL
Age1L
Lifetime score
Lambs
TRLT
R / dLT
R / dPL
R / dUL
LT 0.02 (0.01) .39 .35 0.05 0.44 0.42 0.48 0.54 0.56 0.87 0.28 0.20 0.18 0.15 PL 0.90 0.04 (0.01) 0.95 0.70 0.50 0.03 0.19 0.45 0.91 0.84 0.93 0.81 0.28 0.21 UL 0.85 0.97 0.05 (0.01) 071 0.57 0.05 0.18 0.44 0.94 0.77 0.90 0.82 0.24 0.14 TMY 0.74 0.85 0.90 0.07 (0.03) 0.92 .72 0.77 0.43 0.71 0.20 0.97 0.94 0.39 0.46 M / dLT 0.48 0.66 0.74 0.91 0.16 (0.04) 0.82 0.86 0.41 0.41 0.27 0.85 0.97 0.45 0.53 M / dPL 0.18 0.14 0.02 0.29 0.46 0.16 (0.03) 0.96 0.06 0.05 0.22 0.55 0.71 0.89 0.79 M / dUL 0.17 0.21 0.25 0.58 0.73 0.81 0.20 (0.06) 0.08 0.18 0.33 0.66 0.85 0.79 0.86 Age1L 0.07 0.15 0.15 0.12 0.21 0.06 0.02 0.13 (0.03) 0.15 0.50 0.42 0.24 0.20 0.23 Lifetime score 0.86 0.97 0.99 0.88 0.71 0.06 0.23 0.14 0.03 (0.01) 0.87 0.94 0.71 0.02 0.35 Lambs 0.81 0.92 0.94 0.86 0.71 0.01 0.26 0.11 0.95 0.03 (0.01) 0.49 0.38 0.54 0.52 TRLT 0.80 0.91 0.95 0.97 0.86 0.17 0.46 0.12 0.94 0.94 0.05 (0.03) 0.91 0.27 0.43 R / dLT 0.53 0.74 0.82 0.90 0.95 0.32 0.58 0.23 0.79 0.84 0.91 0.11 (0.03) 0.28 0.44 0.09 0.14 0.27 0.86 0.58 0.11 0.12 0.01 0.10 0.23 0.06 (0.02) 0.89 R / dPL 0.25 0.21 R / dUL 0.19 0.23 0.25 0.52 0.61 0.68 0.84 0.08 0.25 0.38 0.49 0.60 0.72 0.11 (0.03) 1
SE for genetic correlations ranged from 0.01 to 0.41. 2LT = Lifetime; PL = productive life; UL = useful life; TMY= total milk yield; M / dLT = milk/day of lifetime; M / dPL = milk/day of productive life; M / dUL = milk/day of useful life; Age1L = age at first lambing; Lifetime score = number of given parities during LT; Interv = average interval between successive lambings; Lambs = lambs sold at weaning during LT; TRLT = total revenue from milk and lambs during lifetime; R / dLT = revenue from milk and lambs/day of lifetime; R / dPL = revenue from milk and lambs/day of productive life; R / dUL = revenue from milk and lambs/day of useful life.
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Table 7 Heritabilities F SE (on the diagonal), genetic correlations1 (above the diagonal) and phenotypic correlations (below the diagonal) among lifetime performance traits2 under the accelerated lambing system
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lambing ewes. This is also recommended for Churra ewes in order to obtain more homogenous reproductive characteristics. This would contribute to improve modelling of lifetime traits.
4. Conclusions Clear differences in phenotypic and genetic parameter estimates were observed for productivity and lifetime traits between annual and accelerated lambing systems. Due to the relatively low fertility, the means for non-productive periods were greater than desired from an economic point-of-view, especially for the accelerated lambing system. Therefore, management to improve reproductive performance is strongly recommended especially for the young high yielding ewes of flocks under the accelerated lambing system. This would contribute to obtaining more homogenous reproductive characteristics, improving modelling of lifetime traits and probably genetic parameters estimation, too. Potential opportunities for genetic improvement increase with better modelling.
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