- Email: [email protected]
The influences of live weight and body condition score of ewe lambs from breeding to lambing on the live weight of their singleton lambs to weaning
Small Ruminant Research 119 (2014) 16–21
Contents lists available at ScienceDirect
Small Ruminant Research journal homepage: www.elsevier.com/locate/smallrumres
Short communication
The influences of live weight and body condition score of ewe lambs from breeding to lambing on the live weight of their singleton lambs to weaning R.A. Corner-Thomas a,∗ , R.E. Hickson a , S.T. Morris a , P.R. Kenyon a,b a International Sheep Research Centre, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand b National Research Centre for Growth and Development, Massey University, Palmerston North 4442, New Zealand
a r t i c l e
i n f o
Article history: Received 29 October 2013 Received in revised form 26 January 2014 Accepted 28 January 2014 Available online 7 February 2014
Keywords: Ewe lamb Reproduction Lamb growth Body condition score
a b s t r a c t One of the limiting factors to the adoption of breeding 7-month-old ewes is that their lambs are lighter at birth and weaning than lambs born to mature ewes. The present study tested the hypothesis that the live weight and body condition score of 7-month-old ewes at breeding and during pregnancy would influence the live weight of their singleton-born lambs to weaning. Data was collected on one commercial sheep farm from 591 ewes across two years. In 2011 and 2012, during pregnancy the ewes gained 14.6 and 10.1 kg of total live weight, respectively. Multiple regression analysis indicated that live weight of ewes at breeding had a positive effect (P < 0.05, 0.03 ± 0.02 kg of birth weight per kg of ewe live weight) on lamb birth weight while ewe live weight in late pregnancy had a negative effect (P < 0.05, −0.03 ± 0.01 kg of birth weight per kg of ewe live weight). Overall the R-square of the model for lamb birth weight was small (R2 = 0.01) indicating, that live weight of the ewe was not a major contributor to the live weight of lambs at birth. The live weight of ewes in late pregnancy had a positive impact on both the live weight of lambs at approximately 18 days of age and at weaning (P < 0.05, 0.05 ± 0.02 and 0.08 ± 0.03 kg of lamb live weight per kg of ewe live weight, respectively) but again the R2 value for the multiple regression was small (0.01). Body condition score of the ewe at breeding and in mid-pregnancy had no effect (P > 0.05) on lamb birth weight. In contrast ewes with body conditions scores of 3.5 and 4.0 or greater in late pregnancy gave birth to lighter lambs (4.9 ± 0.1 and 4.7 ± 0.2 kg, respectively) than ewes with body condition scores of 2.5 or less (5.3 ± 0.1 kg) or 3.0 (5.2 ± 0.1 kg, P < 0.05). There was no effect (P > 0.05) of ewe body condition score on lamb live weight at approximately 18 days of age or at weaning. Therefore, under the conditions of this study ewe live weight and condition score during pregnancy had a minimal effect of lamb live weight from birth to weaning. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Breeding ewes to lamb at one year of age is a potential means of improving farm profitability and ewe
∗ Corresponding author at: Private Bag 11222, Palmerston North 4442, New Zealand. Tel.: +64 63569099x85179; fax: +64 63505714. E-mail address: [email protected] (R.A. Corner-Thomas). 0921-4488/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.smallrumres.2014.01.008
lifetime performance (Kenyon et al., 2011c; Young et al., 2010). However, less than 40% of 7-month-old ewes are bred each year in Australia and New Zealand, indicating that ewe lamb breeding can be a difficult practise for farmers to utilise (Anonymous, 2013; Curtis and Croker, 2005). The aims of a ewe breeding program utilising breeding of 7-month-old ewes should include the successful weaning of a lamb that is as heavy as possible.
R.A. Corner-Thomas et al. / Small Ruminant Research 119 (2014) 16–21
Live weights and survival rates of lambs born to ewes bred at 7-month of age are often lower than those born to mature ewes (Corner et al., 2013). The birth weight of a lamb can affect its survival chances, with lower survival rates observed at the birth weight extremes (Hatcher et al., 2009; Knight et al., 1988; Thompson et al., 2004). In addition, the weight of the lamb at birth influences its weaning weight (Kenyon et al., 2004a) and low weaning weights of lambs born were identified by farmers as a limiting factor for breeding 7-month-old ewes (Kenyon et al., 2004b). It has been established that the live weight and body condition of the mature ewe can affect both lamb birth and weaning live weight (Hickson et al., 2012; Kenyon et al., 2004a; Oldham et al., 2011). Using a meta-analytic approach of data from many studies, Schreurs et al. (2010b) reported that, when breeding 7-month-old ewes, increased live weight at breeding and during pregnancy had a positive effect on the live weight of their offspring. However, in that analysis no attempt was made to correct for the potential influence of the conceptus mass on total live weight of the ewe in pregnancy. Currently the impact of body condition of 7-month-old ewes on the live weight of their lamb is unknown. As a result there are no guidelines which farmers can use to determine the optimum live weight and body condition score that ewe lambs should achieve prior to breeding. Therefore, the aim of the present study was to test the hypothesis that the conceptus-free live weight and body condition score of ewes 7-month-old at breeding would have a positive influence on the live weight of her offspring to weaning. 2. Materials and methods 2.1. Animals Over two years, two cohorts of singleton bearing 7-month-old Highlander® composite (½ Romney, ¼ New Zealand Texel and ¼ Finn) ewes were monitored from the beginning of breeding through to the end of their first lactation. The animals were grazed under commercial conditions on a farm located in the lower North Island of New Zealand (40◦ 56 S, 175◦ 42 E). Breeding began on the 29th April in 2011 and on the 1st May in 2012. In both years, only ewes that achieved the minimum live weight of 38 kg were bred. Ewes were bred with composite hogget rams (¼ Suffolk, ¼ Texel and ½ Dorper) at a ratio of 1:65 for a 34-day period. At the end of the breeding period, rams were removed and each cohort of ewes was managed as a single flock under commercial farming conditions until weaning of their lambs. Throughout pregnancy and lactation ewes were offered ryegrass pastures of between 1100 and 1500 kg DM/ha. Pregnancy diagnosis was determined (non-pregnant, single or twin-bearing) using trans-abdominal ultrasound in mid-pregnancy (approximately 88 days after start of breeding in 2011 and 85 days in 2012). In both years, a second pregnancy diagnosis was conducted using the same technique in late-pregnancy (139 and 135 days after the start of breeding in 2011 and 2012, respectively). The present study considered only singleton-bearing ewes which were confirmed as pregnant at both pregnancy diagnoses. Therefore, the study presented here includes 295 and 294 ewe-lamb pairs from 2011 and 2012, respectively. In 2011, lambing began on the 17th September and finished on the 27th October. In 2012, lambing began on the 23rd September and finished on the 26th October. Lambs were weaned as per standard farm practice on the 12th January 2011 and 14 January 2012 (97 days after the mid-point of the lambing period, L97). 2.2. Measurements taken In 2011 and 2012, all ewes were weighed un-fasted on the day of ram introduction (start of breeding), at the removal of the ram (end of
17
breeding), 88 and 85 days after the start of breeding in 2011 and 2012, respectively (mid-pregnancy), and 139 and 135 days after the start of breeding in 2011 and 2012, respectively (late pregnancy). In addition, ewe body condition scores (BCS, Jefferies, 1961, scale 1–5, 1 = emaciated, 5 = obese) were recorded at the start of breeding, and in mid- and latepregnancy. At the start of the breeding period in 2011, ewe live weights ranged from 38.0 to 56.6 kg (mean = 44.7 kg) and BCS ranged from 2.0 to 4.5. In 2012, live weights at breeding ranged from 38.0 to 53.5 kg (mean = 43.1 kg) and BCS from 2.0 to 4.0. During the lambing period, ewes were observed twice daily. Lambs, regardless of whether they were born alive or dead, were tagged with a uniquely numbered ear tag and were identified to their dam. At the time of ear tagging, the sex of the lamb and its birth weight were recorded. Live lambs less than 4 h of age were left untagged until the next observation period to allow the ewe and lamb to bond. During the lactation period, additional lamb live weights were recorded at an average age of 18 days in 2011 and 17 days in 2012 and at an average age of 97 days in both years (weaning). Lambs were recorded as dead if they were not present at weaning. 2.3. Statistical analyses All statistical analyses were conducted using SAS (SAS Institute Inc., Cary, NC, USA). 2.3.1. Conceptus-free live weights In order to eliminate the influence of conceptus weight on ewe live weight in pregnancy, predicted conceptus-free live weights of ewes were used in the analyses. Ewe conceptus-free live weights at the end of breeding and in mid- and late-pregnancy were adjusted by subtracting the estimated weight of the conceptus. The weight of the conceptus was estimated based on lamb birth weight using the equations from the GRAZPLAN model (Freer et al., 1997). To estimate ‘days pregnant’ it was assumed that all pregnancies were 146 days in length and therefore 146 days minus the difference between the date of weighing and the date of lambing was the total number of days pregnant. This method of estimating the weight of the conceptus has previously been used in studies of mature ewes by John et al. (2011) and Paganoni et al. (in press). Failure to remove the weight of the conceptus can have a confounding effect as a heavier lamb at birth would be likely to have a greater foetal weight at a given point in time and therefore result in a heavier total ewe live weight. Conceptus weight = lamb’s birth weight × 1.43e3.38(1−e
0.91(1−(days pregnant/146)) )
2.3.2. Comparison of years The effect of year on ewe live weight and lamb live weight was analysed using a general linear model. The models of ewe live weight contained the fixed effect of year (2011 and 2012). Models of lamb live weight contained the fixed effects of year and sex of the lamb and also contained day of birth relative to the mid-point of the lambing period as a covariate. The effect of year on ewe body condition scores was analysed using a generalised model based on a Poisson distribution and a logit transformation. The effect of year on lamb survival to weaning was analysed using a generalised model using a binomial distribution and a logit transformation. The model of lamb survival contained the fixed effects of year and the sex of the lamb. 2.3.3. Effect of ewe live weight on lamb live weight The effect of ewe live weight on lamb live weight (at birth, ∼18 days of age, weaning) was determined using a step-wise multiple regression analysis. Step-wise regressions were conducted using the residual of lamb live weights generated from the general linear model used in the comparison of years. In order to calculate the solution to the multiple regression models the overall mean, which was determined from the general linear model, was added to the residual of the lamb live weights. 2.3.4. Effect of ewe BCS on lamb live weight The effect of ewe BCS on lamb live weight at each time point (birth, ∼18 days of age, weaning) was determined using general linear models. Due to low numbers of ewes with a BCS of 2, these ewes were combined with ewes with a BCS of 2.5 to create a group BCS ≤ 2.5. Grouping also
18
R.A. Corner-Thomas et al. / Small Ruminant Research 119 (2014) 16–21
Table 1 Multiple regression coefficients for the relationship of calculated conceptus-free live weight of ewes at the start of breeding and late-pregnancy with the residuals of lamb live weight at birth, approximately 18 days of age and at weaning. Where no value is given the coefficient was not significant in the multiple regression model.
Birthb ∼18 days of age Weaning
Meana
Intercept
Live weight of ewe at start of breeding
Live weight of ewe in late-pregnancy
R2
5.1 18.0 30.5
0.41 ± 0.63 −2.44 ± 1.13 −3.95 ± 1.66
0.03 ± 0.02
−0.03 ± 0.01 0.05 ± 0.02 0.08 ± 0.03
0.014 0.010 0.013
a
Means listed were produced by the general linear model used to generate the residuals included in the regression. Multiple regression equations can be derived from this table by assembling the various components for example: lamb birth weight = 5.1 + 0.41(±0.63) + 0.03(±0.02) × live weight of the ewe at start of breeding − 0.03(±0.01) × live weight of the ewe in late pregnancy. b
occurred with ewes of BCS of 4 and 4.5 to create BCS ≥ 4. Each model contained the fixed effects of year and the sex of the lamb and ewe body condition score and their interactions. All two- and three-way interactions were included in the initial models and any non-significant interactions were removed and the models were re-run. The models were run both with and without the inclusion of the corresponding ewe live weight as a covariate in order to determine if the apparent differences observed were due to differences in ewe live weight.
3. Results 3.1. Description of years At the start of the breeding period, ewes were heavier (P < 0.05) in 2011 than in 2012 (44.7 ± 0.17 kg vs. 43.1 ± 0.18 kg, respectively) and tended (P = 0.08) to have a higher BCS (3.2, 3.0–3.4 vs. 2.9, 2.7–3.1, respectively). From breeding until late-pregnancy, ewes gained more (P < 0.05) weight in 2011 than in 2012 (14.6 ± 0.2 kg vs. 10.1 ± 0.2 kg, respectively). The live weight of ewes in late-pregnancy (∼day 135 of pregnancy) was 59.3 ± 0.3 kg in 2011 and 53.3 ± 0.3 kg in 2012. These live weights equated to conceptus-free live weights of 53.2 ± 0.3 and 48.2 ± 0.3 kg, respectively. The body condition scores of ewes in late-pregnancy were greater (P < 0.05) in 2011 than 2012 at 3.2 (3.0–3.4) and 2.9 (2.7–3.1), respectively. Lambs born in 2011 were heavier (P < 0.05) than lambs born in 2012 at birth (5.4 ± 0.1 kg vs. 4.9 ± 0.1 kg, respectively) and at approximately 18 days of age (19.8 ± 0.2 kg vs. 16.4 ± 0.2 kg, respectively) but were lighter (P < 0.05) at weaning (30.0 ± 0.2 kg vs. 31.3 ± 0.2 kg, respectively). Lamb survival did not differ (P > 0.05) between years at 82.7% (79.4–87.8%) in 2011 and 79.7% (73.1–82.8%) in 2012.
with increasing ewe live weight in late-pregnancy (P < 0.05, Table 1), although the absolute changes were minor. For example, the regression coefficient of the calculated conceptus-free live weight of ewes at the start of breeding indicates that lamb live weight at birth would be 30 g heavier for every additional kilogram of ewe calculated conceptus-free live weight at the start of the breeding period. While the regression coefficient of the calculated conceptus-free live weight of ewes in late pregnancy indicates that lamb live weights at birth would be 34 g lighter for every additional kilogram of calculated conceptus-free live weight in late-pregnancy. 3.2.2. Lamb live weight at approximately 18 days of age The live weight of lambs at approximately 18 days of age increased with increasing calculated conceptus-free live weight of ewes in late-pregnancy (P < 0.05, Table 1), but again the absolute changes were relatively minor. The regression coefficient of calculated conceptus-free ewe live weight in late pregnancy indicated lambs would be 47 g heavier at approximately 18 days of age for every additional kilogram of ewe calculated conceptus-free live weight in late-pregnancy. 3.2.3. Lamb live weight at weaning Lamb live weight at weaning increased with increasing ewe live weight in late-pregnancy (P < 0.05, Table 1). As with the earlier models the absolute effects were minimal. The regression coefficient of conceptus-free live weight of ewes in late pregnancy indicated that lambs would be an additional 77 g heavier at weaning for every additional kilogram live weight.
3.2. Effect of conceptus-free live weight of ewes
3.3. Effect of ewe body condition score
All multiple regression models generated in this analysis, although statistically significant (P < 0.05), had relatively small overall R2 values and, therefore, only explained a small proportion of the variability (1.0–1.3%) in the variable of interest (Table 1). The calculated conceptusfree live of ewes at the end of breeding period and in mid-pregnancy was not significant (P > 0.05) in any of the models for live weight of the lamb and therefore are not included in the final models.
3.3.1. Lamb live weight at birth Ewe BCS at breeding and in mid-pregnancy had no effect on lamb birth weight (P > 0.05). In contrast, the BCS of the ewe in late-pregnancy influenced lamb birth weight such that ewes with BCS ≤ 2.5 or 3 gave birth to heavier lambs than ewes with a BCS3.5 or BCS ≥ 4 (P < 0.05, Table 2). The inclusion of the calculated conceptus-free live weight of ewes in late-pregnancy as a covariate in the model resulted in the differences between BCS3.5 and both BCS ≤ 2.5 and BCS3 becoming non-significant (P > 0.05) It did not, however, alter the significant differences of BCS ≥ 4 with BCS ≤ 2.5 and BCS3 (P < 0.05). The inclusion of the covariate resulted in the means for BCS ≤ 2.5,
3.2.1. Lamb live weight at birth Lamb weight at birth increased with increasing ewe live weight at the start of breeding (P < 0.05) but decreased
R.A. Corner-Thomas et al. / Small Ruminant Research 119 (2014) 16–21
19
Table 2 The effect of ewe body condition score (BCS) at the start of breeding, in mid-pregnancy and late-pregnancy on lamb live weight (kg; mean ± SEM) at birth, approximately 18 days of age and weaning. Lamb live weight
Birth ∼18 days of age Weaning
BCS of ewes at start of breedinga ≤2.5
3
3.5
≥4
5.2 ± 0.1 17.7 ± 0.3 30.4 ± 0.4
5.1 ± 0.1 18.0 ± 0.2 30.5 ± 0.3
5.0 ± 0.1 18.5 ± 0.2 31.1 ± 0.4
5.4 ± 0.2 18.2 ± 0.6 30.5 ± 0.7
BCS of ewes in mid-pregnancy
Birth ∼18 days of age Weaning
≤2.5
3
3.5
≥4
5.2 ± 0.1 17.7 ± 0.3 30.1 ± 0.3
5.0 ± 0.1 18.4 ± 0.3 31.0 ± 0.3
5.1 ± 0.1 18.5 ± 0.4 31.1 ± 0.5
5.0 ± 0.2 17.9 ± 0.5 30.8 ± 0.6
3
3.5
≥4
BCS of ewes in late pregnancy ≤2.5 Birth ∼18 days of age Weaning a
5.3 ± 0.1 18.2 ± 0.3 30.5 ± 0.4
b
5.2 ± 0.1 18.0 ± 0.2 30.7 ± 0.3
b
4.9 ± 0.1 18.2 ± 0.4 30.6 ± 0.4
a
4.7 ± 0.2a 17.8 ± 0.6 30.3 ± 0.7
Means within rows with differing superscripts are significantly different (P < 0.05).
BCS3.5 and BCS ≥ 4, changing to 5.2 ± 0.1, 5.0 ± 0.1 and 4.8 ± 0.2 kg, respectively, while the mean of BCS3 remained unchanged.
3.3.2. Lamb live weight at approximately 18 days of age Ewes with BCS ≤ 2.5 at breeding had lambs that tended to be lighter at approximately 18 days of age than ewes with BCS3.5 (P = 0.06, Table 2). The inclusion of the calculated conceptus-free live weight of the ewe at the start of breeding did not alter the means of these lambs or remove the tendency observed (P = 0.08). Ewes with BCS ≤ 2.5 in midpregnancy tended to have lighter lambs at approximately 18 days of age than ewes with BCS3 (P = 0.06). However, the inclusion of the calculated conceptus-free live weight of ewes in mid-pregnancy resulted in this tendency becoming non-significant (P>0.05). Ewe BCS in late pregnancy had no effect on lamb live weight at approximately 18 days of age (P > 0.05, Table 2). However, after the inclusion of the calculated conceptus-free live weight in late-pregnancy, ewes with BCS ≤ 2.5 had heavier lambs at approximately 18 days of age (18.6 ± 0.3 kg; P < 0.05) than ewes with BCS3.5 (17.6 ± 0.3 kg) and tended to be heavier than lambs born to ewes with BCS3 (18.0 ± 0.2 kg; P = 0.08) and BCS ≥ 4 (17.4 ± 0.6 kg; P = 0.07).
3.3.3. Lamb live weight at weaning Ewe BCS at breeding and late-pregnancy had no effect on lamb live weight at weaning both with, and without, calculated conceptus-free live weight of the ewe as a covariate (P > 0.05, Table 2). Ewes with BCS ≤ 2.5 in mid-pregnancy tended to have lighter lambs at weaning than ewes with BCS3 (P = 0.06), however, the inclusion of ewe live weight in the model resulted in this tendency becoming nonsignificant (data not shown).
4. Discussion The aim of the present study was to determine the impact of ewe live weight and body condition score at breeding and during pregnancy on the live weight of lambs to weaning. To reduce the potential confounding effects of the conceptus mass on live weight of lambs the ewe live weights used for the analyses were corrected for predicted conceptus weight. In addition, the aim of the study was not to compare the performance across years, however, that data was presented to allow for understanding of the conditions during the study. Overall, the models used to describe lamb birth weight explained only a small proportion of the total variation, indicating ewe live weight had only a minor influence. The small positive effect of ewe live weight at breeding on lamb birth weight complements the relatively minimal impacts previously reported for mature ewes (Hickson et al., 2012; Kenyon et al., 2004a; Oldham et al., 2011) and 7-monthold ewes (Schreurs et al., 2010b). Combined, these results indicate that although 7-month-old ewe live weight could be used as a management tool to manipulate lamb birth weight the influence would be small. Ewe body condition score at breeding had no impact on lamb birth weight which supports the findings for mature ewes by Aliyari et al. (2012) but contrast with those of Kenyon et al. (2004a) who reported a negative effect of very high body condition scores. These results suggest ewe body condition score at breeding may not be a suitable tool for the manipulation of lamb birth weight. Interestingly, ewe live weight in late pregnancy had a negative effect on lamb birth weight. The result is supported by the findings of Wallace (2000) and Wallace et al. (2008) that nutritional regimens which resulted in greater ewe live weights at term were associated with lighter lamb birth weights. However, this apparent negative effect on birth weight is small and would not be large enough to
20
R.A. Corner-Thomas et al. / Small Ruminant Research 119 (2014) 16–21
move these lambs outside the optimal live weight range of 3.5–5.5 kg for survival (Dalton et al., 1980; Nowak and Poindron, 2006). In contrast to the present study, Schreurs et al. (2010b) reported a small positive influence of late pregnancy ewe live weight on lamb birth weight. However, that analysis was potentially confounded by the weight of the conceptus, as no attempt was made to correct for this. The calculated conceptus-free live weight of the ewe in late-pregnancy explained only a small proportion of the total variation in the live weight of lambs in early lactation and at weaning. The positive effect of ewe live weight in late pregnancy on lamb weaning weight was of similar magnitude of that reported in ewe lambs by Schreurs et al. (2010b). In addition, Kenyon et al. (2008), Morris et al. (2005) and Mulvaney et al. (2010) reported that in 7-month-old ewes greater levels of pregnancy nutrition, which led to heavier live weights in late pregnancy, had a positive influence on lamb weaning weight. The results of these studies combined indicate manipulating ewe lamb live weight is a means to increase weaning weights of lambs. Across the entire range of BCS observed, the influence of ewe BCS on lamb live weight at approximately 18 days of age and weaning was never greater than 1.0 kg indicating BCS had only minimal impact. This suggests that ewe BCS cannot be used as a tool for farmers to appreciably alter lamb live weight. In addition it was observed that inclusion of ewe live weight often reduced the effect observed from BCS indicating live weight was a driving factor in the response. In mature ewes, BCS has either had no effect on lamb weaning weight or very poor BCS was associated with lower weaning weights (Al-Sabbagh et al., 1995; Kenyon et al., 2011a; Sejian et al., 2009). Ewe live weight and BCS in this present study had minimal impact on lamb live weight as outlined above. Therefore, it is important to consider why this might have been the case. Loureiro et al. (2010) reported that the gravid uterine weight of a singleton bearing ewe lamb carrying a foetus of 5.1 kg within a week of parturition weighed less than 9 kg. In both years of the present study, ewes gained total live weight at a level greater than this. Therefore, the ewes were unlikely to have been required to draw on their own reserves to meet the additional requirements of pregnancy. This may explain the relatively small impact of both ewe live weight and BCS on lamb live weight. Another contributing factor may have been the minimum breeding weight of 38 kg. It would be of interest to determine if the effects of ewe live weight and BCS would be greater under conditions in which the ewes gained less total live weight in pregnancy or were lighter at breeding. 5. Conclusion Under the conditions of the present study both ewe live weight and body condition at breeding and in pregnancy had only a minimal influence on lamb live weight to weaning. This indicates that manipulation of ewe live weight and body condition is not a means farmers can use to significantly alter lamb live weights. However, further studies to determine whether similar results are observed under conditions in which ewes were either lighter at breeding
and/or gained less total live weight in pregnancy would be worthwhile. Acknowledgements This study was supported by Gravida through the part funding of the position held by P.R. Kenyon and by the C Almer Baker Trust for the part funding of the position held by R.A. Corner-Thomas. The authors wish to acknowledge the help provided by the Taratahi Agricultural Training Centre staff and students. References Aliyari, D., Moeini, M.M., Shahir, M.H., Sirijani, M.A., 2012. Effect of body condition score, live weight and age on reproductive performance of Afshari ewes. Asian J. Anim. Vet. Adv. 7, 904–909. Al-Sabbagh, T.A., Swanson, L.V., Thompson, J.M., 1995. The effect of body condition at lambing on colostral immunoglobulin G concentration and lamb performance. J. Anim. Sci. 73, 2860–2864. Anonymous, 2013. Ministry for Primary Industries, Livestock Statistics, www.mpi.govt.nz/news-resources/statistics-forecasting/livestockstatistics.aspx (accessed 25.03.13). Corner, R.A., Mulvaney, F.J., Morris, S.T., West, D.M., Morel, P.C.H., Kenyon, P.R., 2013. A comparison of the reproductive performance of ewe lambs and mature ewes. Small Rumin. Res. 114, 126–133. Curtis, K., Croker, K., 2005. Wool desk report, September 2005. Department of Agriculture and Food, Western Australia, p. 17. Dalton, D.C., Knight, T.W., Johnson, D.L., 1980. Lamb survival in sheep breeds on New Zealand hill country. N. Z. J. Agric. Res. 23, 167–173. Freer, M., Moore, A.D., Donnelly, J.R., 1997. GRAZPLAN: decision support systems for Australian grazing enterprises. II. The animal biology model for feed intake, production and reproduction and the GrazFeed DSS. Agric. Syst. 54, 77–126. Hatcher, S., Atkins, K.D., Safari, E., 2009. Phenotypic aspects of lamb survival in Australian Merino Sheep. J. Anim. Sci. 87, 2781–2790. Hickson, R.E., Kenyon, P.R., Blair, H.T., Harding, J.E., Oliver, M.H., Jaquiery, A.L., Nicoll, G.B., Burt, K.G., 2012. The effect of liveweight and liveweight gain of ewes immediately post-weaning on the liveweight and survival of subsequent lambs. Anim. Prod. Sci. 52 (6–7), 491–496. Jefferies, B.C., 1961. Body condition scoring and its use in management. Tasmanian J. Agric. 32, 19–22. John, S.E., Ferguson, M.B., Gardner, G.E., Thompson, A.N., 2011. Fluctuation in ewe liveweight during periods of restricted nutrition is influenced by sire. Proc. Assoc. Adv. Anim. Genet. 19, 450–453. Kenyon, P.R., Morel, P.C.H., Morris, S.T., 2004a. Effect of ewe liveweight and condition score at mating, and mid-pregnancy shearing, on birthweights and growth rates of twin lambs to weaning. N. Z. Vet. J. 52, 145–149. Kenyon, P.R., Morris, S.T., Perkins, N.R., West, D.M., 2004b. Hogget mating use in New Zealand – a survey. Proc. N. Z. Soc. Anim. Prod. 64, 217–222. Kenyon, P.R., Morris, S.T., West, D.M., 2008. Effects of nutrition during pregnancy on hogget pregnancy outcome and birthweight and liveweights of lambs. N. Z. J. Agric. Res. 51, 77–83. Kenyon, P.R., Morris, S.T., Stafford, K.J., West, D.M., 2011a. The effect of ewe body condition and nutrition in late pregnancy on the performance of triplet-bearing ewes and their progeny. Anim. Prod. Sci. 51, 557–564. Kenyon, P.R., van der Linden, D.S., West, D.M., Morris, S.T., 2011c. The effect of breeding hoggets on lifetime performance. N. Z. J. Agric. Res. 54, 321–330. Knight, T.W., Lynch, P.R., Hall, D.R.H., Hockey, H.U.B., 1988. Identification of factors contributing to the improved lamb survival in Marshall Romney sheep. N. Z. J. Agric. Res. 31, 259–271. Loureiro, M.F.P., Pain, S.J., Kenyon, P.R., Blair, H.T., 2010. Do fetuses from primiparous one-year-old ewes differ from those of multiparous mature ewes? Proc. N. Z. Soc. Anim. Prod. 70, 118–120. Morris, S.T., Kenyon, P.R., West, D.M., 2005. Effect of hogget nutrition in pregnancy on lamb birth weight and survival to weaning. N. Z. J. Agric. Res. 48, 165–175. Mulvaney, F.J., Morris, S.T., Kenyon, P.R., Morel, P.C.H., West, D.M., 2010. Effect of nutrition pre-breeding and during pregnancy on breeding performance of ewe lambs. Anim. Prod. Sci. 50, 953–960. Nowak, R., Poindron, P., 2006. From birth to colostrum: early steps leading to lamb survival. Reprod. Nutr. Dev. 46, 431–446.
R.A. Corner-Thomas et al. / Small Ruminant Research 119 (2014) 16–21 Oldham, C.M., Thompson, A.N., Ferguson, M.B., Gordon, D.J., Kearney, G.A., Paganoni, B.L., 2011. The birthweight and survival of merino lambs can be predicted from the profile of live weight change of their mothers during pregnancy. Anim. Prod. Sci. 51, 776–783. Paganoni, B.L., Ferguson, M.B., Ferrio, S., Jones, C., Kearney, G.A., Kenyon, P.R., Macleay, C., Vinoles, C., Thompson, A.N. Early reproductive losses are a major factor contributing to the poor reproductive performance of Merino ewe lambs mated at 8 to 10 months of age, Anim. Prod. Sci., in press. Schreurs, N.M., Kenyon, P.R., Morel, P.C.H., West, D.M., Morris, S.T., 2010b. Response of additional ewe liveweight during gestation on the birth weight and weaning weight of offspring and weight of the ewe lamb at weaning. Anim. Prod. Sci. 50, 528–532. Sejian, V., Maurya, V.P., Naqvi, S.M.K., Kumar, D., Joshi, A., 2009. Effect of induced body condition score differences on physiological response, productive and reproductive performance of Malpura ewes kept
21
in a hot, semi-arid environment. J. Anim. Physiol. Anim. Nutr. 94, 154–161. Thompson, B.C., Muir, P.D., Smith, N.B., 2004. Litter size, lamb survival, birth and twelve week weight in lambs born to cross-bred ewes. Proc. N. Z. Grassl. Assoc. 66, 233–237. Young, J.M., Thompson, A.N., Kennedy, A.J., 2010. Bioeconomic modelling to identify the relative importance of a range of critical control points for prime lamb production systems in south-west Victoria. Anim. Prod. Sci. 50, 748–756. Wallace, J.M., 2000. Nutrient partitioning during pregnancy: adverse gestational outcome in overnourished adolescent dams. Proc. Nutr. Soc. 59, 107–117. Wallace, J.M., Milne, J.S., Matsuzaki, M., Aitken, R.P., 2008. Serial measurement of uterine blood flow from mid to late gestation in growth restricted pregnancies induced by overnourishing adolescent sheep dams. Placenta 29, 718–724.
Contents lists available at ScienceDirect
Small Ruminant Research journal homepage: www.elsevier.com/locate/smallrumres
Short communication
The influences of live weight and body condition score of ewe lambs from breeding to lambing on the live weight of their singleton lambs to weaning R.A. Corner-Thomas a,∗ , R.E. Hickson a , S.T. Morris a , P.R. Kenyon a,b a International Sheep Research Centre, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand b National Research Centre for Growth and Development, Massey University, Palmerston North 4442, New Zealand
a r t i c l e
i n f o
Article history: Received 29 October 2013 Received in revised form 26 January 2014 Accepted 28 January 2014 Available online 7 February 2014
Keywords: Ewe lamb Reproduction Lamb growth Body condition score
a b s t r a c t One of the limiting factors to the adoption of breeding 7-month-old ewes is that their lambs are lighter at birth and weaning than lambs born to mature ewes. The present study tested the hypothesis that the live weight and body condition score of 7-month-old ewes at breeding and during pregnancy would influence the live weight of their singleton-born lambs to weaning. Data was collected on one commercial sheep farm from 591 ewes across two years. In 2011 and 2012, during pregnancy the ewes gained 14.6 and 10.1 kg of total live weight, respectively. Multiple regression analysis indicated that live weight of ewes at breeding had a positive effect (P < 0.05, 0.03 ± 0.02 kg of birth weight per kg of ewe live weight) on lamb birth weight while ewe live weight in late pregnancy had a negative effect (P < 0.05, −0.03 ± 0.01 kg of birth weight per kg of ewe live weight). Overall the R-square of the model for lamb birth weight was small (R2 = 0.01) indicating, that live weight of the ewe was not a major contributor to the live weight of lambs at birth. The live weight of ewes in late pregnancy had a positive impact on both the live weight of lambs at approximately 18 days of age and at weaning (P < 0.05, 0.05 ± 0.02 and 0.08 ± 0.03 kg of lamb live weight per kg of ewe live weight, respectively) but again the R2 value for the multiple regression was small (0.01). Body condition score of the ewe at breeding and in mid-pregnancy had no effect (P > 0.05) on lamb birth weight. In contrast ewes with body conditions scores of 3.5 and 4.0 or greater in late pregnancy gave birth to lighter lambs (4.9 ± 0.1 and 4.7 ± 0.2 kg, respectively) than ewes with body condition scores of 2.5 or less (5.3 ± 0.1 kg) or 3.0 (5.2 ± 0.1 kg, P < 0.05). There was no effect (P > 0.05) of ewe body condition score on lamb live weight at approximately 18 days of age or at weaning. Therefore, under the conditions of this study ewe live weight and condition score during pregnancy had a minimal effect of lamb live weight from birth to weaning. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Breeding ewes to lamb at one year of age is a potential means of improving farm profitability and ewe
∗ Corresponding author at: Private Bag 11222, Palmerston North 4442, New Zealand. Tel.: +64 63569099x85179; fax: +64 63505714. E-mail address: [email protected] (R.A. Corner-Thomas). 0921-4488/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.smallrumres.2014.01.008
lifetime performance (Kenyon et al., 2011c; Young et al., 2010). However, less than 40% of 7-month-old ewes are bred each year in Australia and New Zealand, indicating that ewe lamb breeding can be a difficult practise for farmers to utilise (Anonymous, 2013; Curtis and Croker, 2005). The aims of a ewe breeding program utilising breeding of 7-month-old ewes should include the successful weaning of a lamb that is as heavy as possible.
R.A. Corner-Thomas et al. / Small Ruminant Research 119 (2014) 16–21
Live weights and survival rates of lambs born to ewes bred at 7-month of age are often lower than those born to mature ewes (Corner et al., 2013). The birth weight of a lamb can affect its survival chances, with lower survival rates observed at the birth weight extremes (Hatcher et al., 2009; Knight et al., 1988; Thompson et al., 2004). In addition, the weight of the lamb at birth influences its weaning weight (Kenyon et al., 2004a) and low weaning weights of lambs born were identified by farmers as a limiting factor for breeding 7-month-old ewes (Kenyon et al., 2004b). It has been established that the live weight and body condition of the mature ewe can affect both lamb birth and weaning live weight (Hickson et al., 2012; Kenyon et al., 2004a; Oldham et al., 2011). Using a meta-analytic approach of data from many studies, Schreurs et al. (2010b) reported that, when breeding 7-month-old ewes, increased live weight at breeding and during pregnancy had a positive effect on the live weight of their offspring. However, in that analysis no attempt was made to correct for the potential influence of the conceptus mass on total live weight of the ewe in pregnancy. Currently the impact of body condition of 7-month-old ewes on the live weight of their lamb is unknown. As a result there are no guidelines which farmers can use to determine the optimum live weight and body condition score that ewe lambs should achieve prior to breeding. Therefore, the aim of the present study was to test the hypothesis that the conceptus-free live weight and body condition score of ewes 7-month-old at breeding would have a positive influence on the live weight of her offspring to weaning. 2. Materials and methods 2.1. Animals Over two years, two cohorts of singleton bearing 7-month-old Highlander® composite (½ Romney, ¼ New Zealand Texel and ¼ Finn) ewes were monitored from the beginning of breeding through to the end of their first lactation. The animals were grazed under commercial conditions on a farm located in the lower North Island of New Zealand (40◦ 56 S, 175◦ 42 E). Breeding began on the 29th April in 2011 and on the 1st May in 2012. In both years, only ewes that achieved the minimum live weight of 38 kg were bred. Ewes were bred with composite hogget rams (¼ Suffolk, ¼ Texel and ½ Dorper) at a ratio of 1:65 for a 34-day period. At the end of the breeding period, rams were removed and each cohort of ewes was managed as a single flock under commercial farming conditions until weaning of their lambs. Throughout pregnancy and lactation ewes were offered ryegrass pastures of between 1100 and 1500 kg DM/ha. Pregnancy diagnosis was determined (non-pregnant, single or twin-bearing) using trans-abdominal ultrasound in mid-pregnancy (approximately 88 days after start of breeding in 2011 and 85 days in 2012). In both years, a second pregnancy diagnosis was conducted using the same technique in late-pregnancy (139 and 135 days after the start of breeding in 2011 and 2012, respectively). The present study considered only singleton-bearing ewes which were confirmed as pregnant at both pregnancy diagnoses. Therefore, the study presented here includes 295 and 294 ewe-lamb pairs from 2011 and 2012, respectively. In 2011, lambing began on the 17th September and finished on the 27th October. In 2012, lambing began on the 23rd September and finished on the 26th October. Lambs were weaned as per standard farm practice on the 12th January 2011 and 14 January 2012 (97 days after the mid-point of the lambing period, L97). 2.2. Measurements taken In 2011 and 2012, all ewes were weighed un-fasted on the day of ram introduction (start of breeding), at the removal of the ram (end of
17
breeding), 88 and 85 days after the start of breeding in 2011 and 2012, respectively (mid-pregnancy), and 139 and 135 days after the start of breeding in 2011 and 2012, respectively (late pregnancy). In addition, ewe body condition scores (BCS, Jefferies, 1961, scale 1–5, 1 = emaciated, 5 = obese) were recorded at the start of breeding, and in mid- and latepregnancy. At the start of the breeding period in 2011, ewe live weights ranged from 38.0 to 56.6 kg (mean = 44.7 kg) and BCS ranged from 2.0 to 4.5. In 2012, live weights at breeding ranged from 38.0 to 53.5 kg (mean = 43.1 kg) and BCS from 2.0 to 4.0. During the lambing period, ewes were observed twice daily. Lambs, regardless of whether they were born alive or dead, were tagged with a uniquely numbered ear tag and were identified to their dam. At the time of ear tagging, the sex of the lamb and its birth weight were recorded. Live lambs less than 4 h of age were left untagged until the next observation period to allow the ewe and lamb to bond. During the lactation period, additional lamb live weights were recorded at an average age of 18 days in 2011 and 17 days in 2012 and at an average age of 97 days in both years (weaning). Lambs were recorded as dead if they were not present at weaning. 2.3. Statistical analyses All statistical analyses were conducted using SAS (SAS Institute Inc., Cary, NC, USA). 2.3.1. Conceptus-free live weights In order to eliminate the influence of conceptus weight on ewe live weight in pregnancy, predicted conceptus-free live weights of ewes were used in the analyses. Ewe conceptus-free live weights at the end of breeding and in mid- and late-pregnancy were adjusted by subtracting the estimated weight of the conceptus. The weight of the conceptus was estimated based on lamb birth weight using the equations from the GRAZPLAN model (Freer et al., 1997). To estimate ‘days pregnant’ it was assumed that all pregnancies were 146 days in length and therefore 146 days minus the difference between the date of weighing and the date of lambing was the total number of days pregnant. This method of estimating the weight of the conceptus has previously been used in studies of mature ewes by John et al. (2011) and Paganoni et al. (in press). Failure to remove the weight of the conceptus can have a confounding effect as a heavier lamb at birth would be likely to have a greater foetal weight at a given point in time and therefore result in a heavier total ewe live weight. Conceptus weight = lamb’s birth weight × 1.43e3.38(1−e
0.91(1−(days pregnant/146)) )
2.3.2. Comparison of years The effect of year on ewe live weight and lamb live weight was analysed using a general linear model. The models of ewe live weight contained the fixed effect of year (2011 and 2012). Models of lamb live weight contained the fixed effects of year and sex of the lamb and also contained day of birth relative to the mid-point of the lambing period as a covariate. The effect of year on ewe body condition scores was analysed using a generalised model based on a Poisson distribution and a logit transformation. The effect of year on lamb survival to weaning was analysed using a generalised model using a binomial distribution and a logit transformation. The model of lamb survival contained the fixed effects of year and the sex of the lamb. 2.3.3. Effect of ewe live weight on lamb live weight The effect of ewe live weight on lamb live weight (at birth, ∼18 days of age, weaning) was determined using a step-wise multiple regression analysis. Step-wise regressions were conducted using the residual of lamb live weights generated from the general linear model used in the comparison of years. In order to calculate the solution to the multiple regression models the overall mean, which was determined from the general linear model, was added to the residual of the lamb live weights. 2.3.4. Effect of ewe BCS on lamb live weight The effect of ewe BCS on lamb live weight at each time point (birth, ∼18 days of age, weaning) was determined using general linear models. Due to low numbers of ewes with a BCS of 2, these ewes were combined with ewes with a BCS of 2.5 to create a group BCS ≤ 2.5. Grouping also
18
R.A. Corner-Thomas et al. / Small Ruminant Research 119 (2014) 16–21
Table 1 Multiple regression coefficients for the relationship of calculated conceptus-free live weight of ewes at the start of breeding and late-pregnancy with the residuals of lamb live weight at birth, approximately 18 days of age and at weaning. Where no value is given the coefficient was not significant in the multiple regression model.
Birthb ∼18 days of age Weaning
Meana
Intercept
Live weight of ewe at start of breeding
Live weight of ewe in late-pregnancy
R2
5.1 18.0 30.5
0.41 ± 0.63 −2.44 ± 1.13 −3.95 ± 1.66
0.03 ± 0.02
−0.03 ± 0.01 0.05 ± 0.02 0.08 ± 0.03
0.014 0.010 0.013
a
Means listed were produced by the general linear model used to generate the residuals included in the regression. Multiple regression equations can be derived from this table by assembling the various components for example: lamb birth weight = 5.1 + 0.41(±0.63) + 0.03(±0.02) × live weight of the ewe at start of breeding − 0.03(±0.01) × live weight of the ewe in late pregnancy. b
occurred with ewes of BCS of 4 and 4.5 to create BCS ≥ 4. Each model contained the fixed effects of year and the sex of the lamb and ewe body condition score and their interactions. All two- and three-way interactions were included in the initial models and any non-significant interactions were removed and the models were re-run. The models were run both with and without the inclusion of the corresponding ewe live weight as a covariate in order to determine if the apparent differences observed were due to differences in ewe live weight.
3. Results 3.1. Description of years At the start of the breeding period, ewes were heavier (P < 0.05) in 2011 than in 2012 (44.7 ± 0.17 kg vs. 43.1 ± 0.18 kg, respectively) and tended (P = 0.08) to have a higher BCS (3.2, 3.0–3.4 vs. 2.9, 2.7–3.1, respectively). From breeding until late-pregnancy, ewes gained more (P < 0.05) weight in 2011 than in 2012 (14.6 ± 0.2 kg vs. 10.1 ± 0.2 kg, respectively). The live weight of ewes in late-pregnancy (∼day 135 of pregnancy) was 59.3 ± 0.3 kg in 2011 and 53.3 ± 0.3 kg in 2012. These live weights equated to conceptus-free live weights of 53.2 ± 0.3 and 48.2 ± 0.3 kg, respectively. The body condition scores of ewes in late-pregnancy were greater (P < 0.05) in 2011 than 2012 at 3.2 (3.0–3.4) and 2.9 (2.7–3.1), respectively. Lambs born in 2011 were heavier (P < 0.05) than lambs born in 2012 at birth (5.4 ± 0.1 kg vs. 4.9 ± 0.1 kg, respectively) and at approximately 18 days of age (19.8 ± 0.2 kg vs. 16.4 ± 0.2 kg, respectively) but were lighter (P < 0.05) at weaning (30.0 ± 0.2 kg vs. 31.3 ± 0.2 kg, respectively). Lamb survival did not differ (P > 0.05) between years at 82.7% (79.4–87.8%) in 2011 and 79.7% (73.1–82.8%) in 2012.
with increasing ewe live weight in late-pregnancy (P < 0.05, Table 1), although the absolute changes were minor. For example, the regression coefficient of the calculated conceptus-free live weight of ewes at the start of breeding indicates that lamb live weight at birth would be 30 g heavier for every additional kilogram of ewe calculated conceptus-free live weight at the start of the breeding period. While the regression coefficient of the calculated conceptus-free live weight of ewes in late pregnancy indicates that lamb live weights at birth would be 34 g lighter for every additional kilogram of calculated conceptus-free live weight in late-pregnancy. 3.2.2. Lamb live weight at approximately 18 days of age The live weight of lambs at approximately 18 days of age increased with increasing calculated conceptus-free live weight of ewes in late-pregnancy (P < 0.05, Table 1), but again the absolute changes were relatively minor. The regression coefficient of calculated conceptus-free ewe live weight in late pregnancy indicated lambs would be 47 g heavier at approximately 18 days of age for every additional kilogram of ewe calculated conceptus-free live weight in late-pregnancy. 3.2.3. Lamb live weight at weaning Lamb live weight at weaning increased with increasing ewe live weight in late-pregnancy (P < 0.05, Table 1). As with the earlier models the absolute effects were minimal. The regression coefficient of conceptus-free live weight of ewes in late pregnancy indicated that lambs would be an additional 77 g heavier at weaning for every additional kilogram live weight.
3.2. Effect of conceptus-free live weight of ewes
3.3. Effect of ewe body condition score
All multiple regression models generated in this analysis, although statistically significant (P < 0.05), had relatively small overall R2 values and, therefore, only explained a small proportion of the variability (1.0–1.3%) in the variable of interest (Table 1). The calculated conceptusfree live of ewes at the end of breeding period and in mid-pregnancy was not significant (P > 0.05) in any of the models for live weight of the lamb and therefore are not included in the final models.
3.3.1. Lamb live weight at birth Ewe BCS at breeding and in mid-pregnancy had no effect on lamb birth weight (P > 0.05). In contrast, the BCS of the ewe in late-pregnancy influenced lamb birth weight such that ewes with BCS ≤ 2.5 or 3 gave birth to heavier lambs than ewes with a BCS3.5 or BCS ≥ 4 (P < 0.05, Table 2). The inclusion of the calculated conceptus-free live weight of ewes in late-pregnancy as a covariate in the model resulted in the differences between BCS3.5 and both BCS ≤ 2.5 and BCS3 becoming non-significant (P > 0.05) It did not, however, alter the significant differences of BCS ≥ 4 with BCS ≤ 2.5 and BCS3 (P < 0.05). The inclusion of the covariate resulted in the means for BCS ≤ 2.5,
3.2.1. Lamb live weight at birth Lamb weight at birth increased with increasing ewe live weight at the start of breeding (P < 0.05) but decreased
R.A. Corner-Thomas et al. / Small Ruminant Research 119 (2014) 16–21
19
Table 2 The effect of ewe body condition score (BCS) at the start of breeding, in mid-pregnancy and late-pregnancy on lamb live weight (kg; mean ± SEM) at birth, approximately 18 days of age and weaning. Lamb live weight
Birth ∼18 days of age Weaning
BCS of ewes at start of breedinga ≤2.5
3
3.5
≥4
5.2 ± 0.1 17.7 ± 0.3 30.4 ± 0.4
5.1 ± 0.1 18.0 ± 0.2 30.5 ± 0.3
5.0 ± 0.1 18.5 ± 0.2 31.1 ± 0.4
5.4 ± 0.2 18.2 ± 0.6 30.5 ± 0.7
BCS of ewes in mid-pregnancy
Birth ∼18 days of age Weaning
≤2.5
3
3.5
≥4
5.2 ± 0.1 17.7 ± 0.3 30.1 ± 0.3
5.0 ± 0.1 18.4 ± 0.3 31.0 ± 0.3
5.1 ± 0.1 18.5 ± 0.4 31.1 ± 0.5
5.0 ± 0.2 17.9 ± 0.5 30.8 ± 0.6
3
3.5
≥4
BCS of ewes in late pregnancy ≤2.5 Birth ∼18 days of age Weaning a
5.3 ± 0.1 18.2 ± 0.3 30.5 ± 0.4
b
5.2 ± 0.1 18.0 ± 0.2 30.7 ± 0.3
b
4.9 ± 0.1 18.2 ± 0.4 30.6 ± 0.4
a
4.7 ± 0.2a 17.8 ± 0.6 30.3 ± 0.7
Means within rows with differing superscripts are significantly different (P < 0.05).
BCS3.5 and BCS ≥ 4, changing to 5.2 ± 0.1, 5.0 ± 0.1 and 4.8 ± 0.2 kg, respectively, while the mean of BCS3 remained unchanged.
3.3.2. Lamb live weight at approximately 18 days of age Ewes with BCS ≤ 2.5 at breeding had lambs that tended to be lighter at approximately 18 days of age than ewes with BCS3.5 (P = 0.06, Table 2). The inclusion of the calculated conceptus-free live weight of the ewe at the start of breeding did not alter the means of these lambs or remove the tendency observed (P = 0.08). Ewes with BCS ≤ 2.5 in midpregnancy tended to have lighter lambs at approximately 18 days of age than ewes with BCS3 (P = 0.06). However, the inclusion of the calculated conceptus-free live weight of ewes in mid-pregnancy resulted in this tendency becoming non-significant (P>0.05). Ewe BCS in late pregnancy had no effect on lamb live weight at approximately 18 days of age (P > 0.05, Table 2). However, after the inclusion of the calculated conceptus-free live weight in late-pregnancy, ewes with BCS ≤ 2.5 had heavier lambs at approximately 18 days of age (18.6 ± 0.3 kg; P < 0.05) than ewes with BCS3.5 (17.6 ± 0.3 kg) and tended to be heavier than lambs born to ewes with BCS3 (18.0 ± 0.2 kg; P = 0.08) and BCS ≥ 4 (17.4 ± 0.6 kg; P = 0.07).
3.3.3. Lamb live weight at weaning Ewe BCS at breeding and late-pregnancy had no effect on lamb live weight at weaning both with, and without, calculated conceptus-free live weight of the ewe as a covariate (P > 0.05, Table 2). Ewes with BCS ≤ 2.5 in mid-pregnancy tended to have lighter lambs at weaning than ewes with BCS3 (P = 0.06), however, the inclusion of ewe live weight in the model resulted in this tendency becoming nonsignificant (data not shown).
4. Discussion The aim of the present study was to determine the impact of ewe live weight and body condition score at breeding and during pregnancy on the live weight of lambs to weaning. To reduce the potential confounding effects of the conceptus mass on live weight of lambs the ewe live weights used for the analyses were corrected for predicted conceptus weight. In addition, the aim of the study was not to compare the performance across years, however, that data was presented to allow for understanding of the conditions during the study. Overall, the models used to describe lamb birth weight explained only a small proportion of the total variation, indicating ewe live weight had only a minor influence. The small positive effect of ewe live weight at breeding on lamb birth weight complements the relatively minimal impacts previously reported for mature ewes (Hickson et al., 2012; Kenyon et al., 2004a; Oldham et al., 2011) and 7-monthold ewes (Schreurs et al., 2010b). Combined, these results indicate that although 7-month-old ewe live weight could be used as a management tool to manipulate lamb birth weight the influence would be small. Ewe body condition score at breeding had no impact on lamb birth weight which supports the findings for mature ewes by Aliyari et al. (2012) but contrast with those of Kenyon et al. (2004a) who reported a negative effect of very high body condition scores. These results suggest ewe body condition score at breeding may not be a suitable tool for the manipulation of lamb birth weight. Interestingly, ewe live weight in late pregnancy had a negative effect on lamb birth weight. The result is supported by the findings of Wallace (2000) and Wallace et al. (2008) that nutritional regimens which resulted in greater ewe live weights at term were associated with lighter lamb birth weights. However, this apparent negative effect on birth weight is small and would not be large enough to
20
R.A. Corner-Thomas et al. / Small Ruminant Research 119 (2014) 16–21
move these lambs outside the optimal live weight range of 3.5–5.5 kg for survival (Dalton et al., 1980; Nowak and Poindron, 2006). In contrast to the present study, Schreurs et al. (2010b) reported a small positive influence of late pregnancy ewe live weight on lamb birth weight. However, that analysis was potentially confounded by the weight of the conceptus, as no attempt was made to correct for this. The calculated conceptus-free live weight of the ewe in late-pregnancy explained only a small proportion of the total variation in the live weight of lambs in early lactation and at weaning. The positive effect of ewe live weight in late pregnancy on lamb weaning weight was of similar magnitude of that reported in ewe lambs by Schreurs et al. (2010b). In addition, Kenyon et al. (2008), Morris et al. (2005) and Mulvaney et al. (2010) reported that in 7-month-old ewes greater levels of pregnancy nutrition, which led to heavier live weights in late pregnancy, had a positive influence on lamb weaning weight. The results of these studies combined indicate manipulating ewe lamb live weight is a means to increase weaning weights of lambs. Across the entire range of BCS observed, the influence of ewe BCS on lamb live weight at approximately 18 days of age and weaning was never greater than 1.0 kg indicating BCS had only minimal impact. This suggests that ewe BCS cannot be used as a tool for farmers to appreciably alter lamb live weight. In addition it was observed that inclusion of ewe live weight often reduced the effect observed from BCS indicating live weight was a driving factor in the response. In mature ewes, BCS has either had no effect on lamb weaning weight or very poor BCS was associated with lower weaning weights (Al-Sabbagh et al., 1995; Kenyon et al., 2011a; Sejian et al., 2009). Ewe live weight and BCS in this present study had minimal impact on lamb live weight as outlined above. Therefore, it is important to consider why this might have been the case. Loureiro et al. (2010) reported that the gravid uterine weight of a singleton bearing ewe lamb carrying a foetus of 5.1 kg within a week of parturition weighed less than 9 kg. In both years of the present study, ewes gained total live weight at a level greater than this. Therefore, the ewes were unlikely to have been required to draw on their own reserves to meet the additional requirements of pregnancy. This may explain the relatively small impact of both ewe live weight and BCS on lamb live weight. Another contributing factor may have been the minimum breeding weight of 38 kg. It would be of interest to determine if the effects of ewe live weight and BCS would be greater under conditions in which the ewes gained less total live weight in pregnancy or were lighter at breeding. 5. Conclusion Under the conditions of the present study both ewe live weight and body condition at breeding and in pregnancy had only a minimal influence on lamb live weight to weaning. This indicates that manipulation of ewe live weight and body condition is not a means farmers can use to significantly alter lamb live weights. However, further studies to determine whether similar results are observed under conditions in which ewes were either lighter at breeding
and/or gained less total live weight in pregnancy would be worthwhile. Acknowledgements This study was supported by Gravida through the part funding of the position held by P.R. Kenyon and by the C Almer Baker Trust for the part funding of the position held by R.A. Corner-Thomas. The authors wish to acknowledge the help provided by the Taratahi Agricultural Training Centre staff and students. References Aliyari, D., Moeini, M.M., Shahir, M.H., Sirijani, M.A., 2012. Effect of body condition score, live weight and age on reproductive performance of Afshari ewes. Asian J. Anim. Vet. Adv. 7, 904–909. Al-Sabbagh, T.A., Swanson, L.V., Thompson, J.M., 1995. The effect of body condition at lambing on colostral immunoglobulin G concentration and lamb performance. J. Anim. Sci. 73, 2860–2864. Anonymous, 2013. Ministry for Primary Industries, Livestock Statistics, www.mpi.govt.nz/news-resources/statistics-forecasting/livestockstatistics.aspx (accessed 25.03.13). Corner, R.A., Mulvaney, F.J., Morris, S.T., West, D.M., Morel, P.C.H., Kenyon, P.R., 2013. A comparison of the reproductive performance of ewe lambs and mature ewes. Small Rumin. Res. 114, 126–133. Curtis, K., Croker, K., 2005. Wool desk report, September 2005. Department of Agriculture and Food, Western Australia, p. 17. Dalton, D.C., Knight, T.W., Johnson, D.L., 1980. Lamb survival in sheep breeds on New Zealand hill country. N. Z. J. Agric. Res. 23, 167–173. Freer, M., Moore, A.D., Donnelly, J.R., 1997. GRAZPLAN: decision support systems for Australian grazing enterprises. II. The animal biology model for feed intake, production and reproduction and the GrazFeed DSS. Agric. Syst. 54, 77–126. Hatcher, S., Atkins, K.D., Safari, E., 2009. Phenotypic aspects of lamb survival in Australian Merino Sheep. J. Anim. Sci. 87, 2781–2790. Hickson, R.E., Kenyon, P.R., Blair, H.T., Harding, J.E., Oliver, M.H., Jaquiery, A.L., Nicoll, G.B., Burt, K.G., 2012. The effect of liveweight and liveweight gain of ewes immediately post-weaning on the liveweight and survival of subsequent lambs. Anim. Prod. Sci. 52 (6–7), 491–496. Jefferies, B.C., 1961. Body condition scoring and its use in management. Tasmanian J. Agric. 32, 19–22. John, S.E., Ferguson, M.B., Gardner, G.E., Thompson, A.N., 2011. Fluctuation in ewe liveweight during periods of restricted nutrition is influenced by sire. Proc. Assoc. Adv. Anim. Genet. 19, 450–453. Kenyon, P.R., Morel, P.C.H., Morris, S.T., 2004a. Effect of ewe liveweight and condition score at mating, and mid-pregnancy shearing, on birthweights and growth rates of twin lambs to weaning. N. Z. Vet. J. 52, 145–149. Kenyon, P.R., Morris, S.T., Perkins, N.R., West, D.M., 2004b. Hogget mating use in New Zealand – a survey. Proc. N. Z. Soc. Anim. Prod. 64, 217–222. Kenyon, P.R., Morris, S.T., West, D.M., 2008. Effects of nutrition during pregnancy on hogget pregnancy outcome and birthweight and liveweights of lambs. N. Z. J. Agric. Res. 51, 77–83. Kenyon, P.R., Morris, S.T., Stafford, K.J., West, D.M., 2011a. The effect of ewe body condition and nutrition in late pregnancy on the performance of triplet-bearing ewes and their progeny. Anim. Prod. Sci. 51, 557–564. Kenyon, P.R., van der Linden, D.S., West, D.M., Morris, S.T., 2011c. The effect of breeding hoggets on lifetime performance. N. Z. J. Agric. Res. 54, 321–330. Knight, T.W., Lynch, P.R., Hall, D.R.H., Hockey, H.U.B., 1988. Identification of factors contributing to the improved lamb survival in Marshall Romney sheep. N. Z. J. Agric. Res. 31, 259–271. Loureiro, M.F.P., Pain, S.J., Kenyon, P.R., Blair, H.T., 2010. Do fetuses from primiparous one-year-old ewes differ from those of multiparous mature ewes? Proc. N. Z. Soc. Anim. Prod. 70, 118–120. Morris, S.T., Kenyon, P.R., West, D.M., 2005. Effect of hogget nutrition in pregnancy on lamb birth weight and survival to weaning. N. Z. J. Agric. Res. 48, 165–175. Mulvaney, F.J., Morris, S.T., Kenyon, P.R., Morel, P.C.H., West, D.M., 2010. Effect of nutrition pre-breeding and during pregnancy on breeding performance of ewe lambs. Anim. Prod. Sci. 50, 953–960. Nowak, R., Poindron, P., 2006. From birth to colostrum: early steps leading to lamb survival. Reprod. Nutr. Dev. 46, 431–446.
R.A. Corner-Thomas et al. / Small Ruminant Research 119 (2014) 16–21 Oldham, C.M., Thompson, A.N., Ferguson, M.B., Gordon, D.J., Kearney, G.A., Paganoni, B.L., 2011. The birthweight and survival of merino lambs can be predicted from the profile of live weight change of their mothers during pregnancy. Anim. Prod. Sci. 51, 776–783. Paganoni, B.L., Ferguson, M.B., Ferrio, S., Jones, C., Kearney, G.A., Kenyon, P.R., Macleay, C., Vinoles, C., Thompson, A.N. Early reproductive losses are a major factor contributing to the poor reproductive performance of Merino ewe lambs mated at 8 to 10 months of age, Anim. Prod. Sci., in press. Schreurs, N.M., Kenyon, P.R., Morel, P.C.H., West, D.M., Morris, S.T., 2010b. Response of additional ewe liveweight during gestation on the birth weight and weaning weight of offspring and weight of the ewe lamb at weaning. Anim. Prod. Sci. 50, 528–532. Sejian, V., Maurya, V.P., Naqvi, S.M.K., Kumar, D., Joshi, A., 2009. Effect of induced body condition score differences on physiological response, productive and reproductive performance of Malpura ewes kept
21
in a hot, semi-arid environment. J. Anim. Physiol. Anim. Nutr. 94, 154–161. Thompson, B.C., Muir, P.D., Smith, N.B., 2004. Litter size, lamb survival, birth and twelve week weight in lambs born to cross-bred ewes. Proc. N. Z. Grassl. Assoc. 66, 233–237. Young, J.M., Thompson, A.N., Kennedy, A.J., 2010. Bioeconomic modelling to identify the relative importance of a range of critical control points for prime lamb production systems in south-west Victoria. Anim. Prod. Sci. 50, 748–756. Wallace, J.M., 2000. Nutrient partitioning during pregnancy: adverse gestational outcome in overnourished adolescent dams. Proc. Nutr. Soc. 59, 107–117. Wallace, J.M., Milne, J.S., Matsuzaki, M., Aitken, R.P., 2008. Serial measurement of uterine blood flow from mid to late gestation in growth restricted pregnancies induced by overnourishing adolescent sheep dams. Placenta 29, 718–724.