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Are calving interval, abortions, incidence of stillbirths and pre-weaning losses in Nguni cows associated with linear type traits?
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Are calving interval, abortions, incidence of stillbirths and pre-weaning losses in Nguni cows associated with linear type traits? T.J. Zindove, M. Chimonyo ∗ Animal and Poultry Science, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, P. Bag X01, Scottsville 3209, Pietermaritzburg, South Africa
a r t i c l e
i n f o
Article history: Received 10 December 2014 Received in revised form 15 June 2015 Accepted 16 July 2015 Available online xxx Keywords: Nguni cows Body depth Calving interval Flank circumference Chest circumference
a b s t r a c t The association of six linear type traits with calving interval, abortions, incidence of stillbirths and pre-weaning losses in Nguni cows in semi-arid and sub-humid communal areas was investigated. It was hypothesised that the odds of a cow having caving interval greater than 1 year, aborting, experiencing stillbirths or losing a calf from calving to weaning decreased with increase in body depth, rump height, flank circumference, chest circumference, navel height and body length. Navel height was measured as the distance from the ground to the lowest point of the cow’s belly bottom (navel). Data were collected from a total of 200 Nguni cows from two sites experiencing sub-humid and semi-arid environments (100 each) between May and June 2013. Cows in sub-humid regions were 2.57 times more likely to have a calving interval of 1 year than cows in semi-arid areas. As body depth increased, the number of calves lost by a cow before weaning decreased linearly (p < 0.05) in all parities except parity 4. Cows in semi-arid regions were 2.13 times more likely to lose a calf from calving to weaning. For each unit increase in body depth, the odds of a cow aborting decreased by 1.12 and the odds of a cow having stillbirth decreased by 1.15. Rump height, flank circumference, chest circumference, navel height and body length were not associated with calving interval, abortions, incidence of stillbirths and pre-weaning losses. It was, therefore, concluded that body depth influences calving interval, incidence of stillbirths and abortions in Nguni cows. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Poor reproductive performance, a challenge of cattle production in rural communal farming systems, has been attributed to low levels of management (Mashoko et al., 2007). Infertility, abortions, stillbirths and high calf mortality rates from birth to weaning are main reproduction constraints to cattle production in communal areas (Mokantla et al., 2004). Low calving percentage can be
∗ Corresponding author. E-mail address: [email protected] (M. Chimonyo).
a result of cows failing to conceive and/or foetal losses (abortions and stillbirths). Stillbirths and abortions have been attributed to various factors including high disease prevalence and poor nutrition (Khodakaram-Tafti and Ikede, 2005). Calving percentages vary yearly due to environmental stresses, such as droughts and fluctuation of environmental temperatures (Gusha et al., 2013); suggesting nutrition and environmental stress play critical roles. In South Africa, the recent quest for viable breeds in communal production systems has resulted in the reintroduction the Nguni breed, a low maintenance breed suitable for low-input systems based on extensive grazing
http://dx.doi.org/10.1016/j.anireprosci.2015.07.002 0378-4320/© 2015 Elsevier B.V. All rights reserved.
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(Bester et al., 2003). The Nguni, a small to medium-framed breed, is extremely hardy and well adapted to harsh environmental conditions of the Southern Sahara. Nguni cattles are resistant to diseases and gastrointestinal parasites, which are among the major causes of low reproductive efficiency in communal cattle production (Ndlovu et al., 2009). Due their adaptation to low quality feeds, Nguni cows have the potential to exhibit high fertility characteristics, such high conception rates, early maturing and short calving intervals. Despite their huge production potential, offtake of Nguni in communal production systems has not yet reached acceptable levels (Musemwa et al., 2010). Low off-take for communal Nguni farmers has been largely attributed to low reproductive efficiency as a result of poor breeding practices, such as poor selection and uncontrolled mating systems (Mapiye et al., 2009). Nqeno et al. (2011) reported that, in South African communal production systems, 65% of farmers have Nguni herds with average calving intervals of 2 years, whilst 55% have cows which experience stillbirths or abortions. Under communal farming systems, calving occur throughout the year. Records are hardly kept and selection of the best individuals is difficult to perform. Communal Nguni farmers rely mostly on memory when selecting breeding cows and/or heifers. They have indigenous knowledge to memorise and acknowledge individual animal and ancestors’ performance (Mgongo et al., 2014). Information on livestock can, however, only be memorised up to a point and can often be forgotten overtime especially when herd composition drastically changes in cases such as drought, disease epidemics and other natural disasters. Considering that written records in communal cattle production are rare and, that memory based selection is not reliable, there is need to come up with complementary strategies to select for reproductive efficiency. Communal farmers use linear traits to complement memory-based selection during selective breeding of cows (Mapiye et al., 2009). High calf mortality rates from birth to weaning of about 30% per annum and long calving intervals of 2 years were, however, estimated in the communal production systems (Nqeno et al., 2011; Nowers et al., 2013). This can be because there is no evidence on the relationship between linear traits and reproductive performance in small-framed beef breeds. In dairy cows, there is a general relationship between the linear traits and reproductive performance (Larroque and Ducrocq, 2001). If the relationship between linear and reproductive efficiency is ascertained, farmers can select breeding cows with ease through visual appraisal. Visual appraisal using linear traits will be cheaper for the poor resource farmers. The objective of the study was to determine whether caving interval, incidence of abortions, incidence of stillbirths and calf mortality in multiparous Nguni cows are associated with linear-type traits. 2. Materials and methods 2.1. Study site The study was conducted in Jozini local municipality, representing sub-humid production environment and
Msinga local municipality representing semi-arid production environment. Both sites are in KwaZulu-Natal province of South Africa. Jozini is located at 27◦ 25 60 S, 32◦ 4 0 E. The altitude is between 150 and 600 m above sea level. The climate is characterised by hot-dry and cool-wet seasons. Annual rainfall averages 600 mm. Most rains are received between January and March, with the months of June and July being dry and cool. Highest mean monthly temperature is recorded in January (30 ◦ C) and lowest in July (11 ◦ C). The vegetation type of the area is mainly coastal sand veld, bush veld and foothill wooded grasslands (Morgenthal et al., 2006). Msinga is located at 28◦ 74 61 S, 30◦ 45 25 E. It receives erratic rainfall and has large daily temperature ranges. The area experiences extremely hot summers with highest mean monthly maximum temperature of 37 ◦ C in January. There is severe cold with frost, with mean monthly minimum temperatures ranging between 4 and 8 ◦ C between May and July. The vegetation type is semi-arid savannah with steep and stony mountains predominated by aloes, thorn bush and some hardwood. 2.2. Data collection A total of 200 multiparous cows were used. Twenty farmers (10 from each region) with at least 10 multiparous Nguni cows in their herd were selected using the snowball technique. The cows were selected on the basis of the owners’ willingness to participate in the study. The cattle grazed on communal rangelands. Measurements were taken during dipping days between May and June 2013. Just before dipping, cattle were held in a race for measurement. A trained person identified 10 Nguni cows from each of the selected farmers’ herds (five young cows and five old cows). The age of the cow was determined by dentition. Cows were divided into two age groups, young (7 years and below)—with visible incisors and old (8 years and above)—with broken or gummy mouth (Raines et al., 2008). The breed score and body condition score (BCS) of the cows were then determined. Visual assessment of the body condition was made using the five-point European system, where a score of 1 is emaciated, and a score of 5 is very fat (Edmonson et al., 1989). Before taking the measurements, each farmer was interviewed on number of calvings (parity of cow), average calving interval (CI), when the cow last calved, when they noticed the cow was pregnant (for pregnant cows), number of stillbirths, when the cow had its last stillbirth, number of abortions, when the cow had its last abortion, number of calves that died before weaning (9 months) and number of calves weaned. Stillbirth was defined as death of a calf at birth or within 24 h of birth after approximately 8 months of gestation or more (Berglund et al., 2003). A cow was considered to have aborted if it gave birth to a dead foetus before 8 months of gestation (Trees et al., 1999). The CI was recorded for cows in parity 3 and above. Reproductive status for each cow was categorised into early pregnancy (less than 3 months), mid pregnancy (4−6 months), late pregnancy (7−9 months), early lactation (less than 3 months), mid lactation (4−6 months) and late lactation (more than 7 months). Interviews were conducted in Zulu vernacular by a trained enumerator. Stillbirths, abortions and calves lost from
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calving to weaning were coded as categorical traits (1 = had stillbirth, 0 = did not have stillbirth; 1 = had an abortion, 0 = did not have an abortion; 1 lost a calf from calving to weaning; 0 = no calf died before weaning). Measurements were taken between 07.00 and 10.00 h before cows had started grazing. Records were taken once from each cow. The measurements taken were rump height, body depth, chest circumference, flank circumference, navel height and body length. The rump height was measured from top of the spine in between hips to the ground. Body depth was measured as distance between the top of spine and bottom of barrel at last rib (the deepest point) measured from the left side of the cow. Chest circumference was defined as circumference of the body taken just behind the shoulders. Flank circumference was defined as circumference of the body taken just in front of the hook bones. Navel height was measured as the distance from the ground to the lowest point of the cow’s belly bottom (navel). Body length was measured from the hindmost part of the animal to the valley in front of the second thoracic vertebrae just ahead of the centre of the shoulders (Alphonsus et al., 2012). Body depth, chest circumference, body length and flank circumference were measured using a plastic tape measure. Navel height and rump height were measured using an aluminium extending measuring stick obtained from Scales 2000 Ltd, Westville, South Africa. To ensure consistency, all measurements were taken by the same individual. Breed scores were assessed visually by the same assessor throughout the experimental period. Each animal was scored using a 1−9 scale based on nine physical characteristics of Nguni cows as described by Nguni breeders association. Each cow would be given a score corresponding to the number of descriptive characteristics it possessed. Physical characteristics considered were: 1: general size of small to medium (rump height less than 130 cm), 2: less developed dewlap and umbilical fold, 3: hardly noticeable cervico-thoracic hump, 4: rump drooping towards tail, 5: moderately dipped forehead constricted just below the horns, 6: wide and slightly convex face, 7: small ears with a sharp apex, 8: small udders and teats, 9: noticeably lyre-shaped horns. A cow was considered for this study only if it met at least five of the nine physical characteristics. A score of five means the cow met five of the nine physical characteristics and a score of nine means that the cow met all the nine characteristics.
2.3. Statistical analyses The effects of production environment and parity of cow on linear traits and total number of calves lost from calving to weaning for each cow (TCL) were analysed using the General Linear Model procedures (SAS, 2008), assuming fixed models with all possible first-, second- and thirdorder interactions. Models for final analyses were obtained after eliminating interactions that were not significant (p > 0.05). The body depth, flank circumference, chest circumference, body length, navel height and rump height were fitted as covariates where relevant. The following models were used:
3
Model 1: Total number of calves lost before weaning for each cow Yijkl = + Pi + ENj + BSk + (BD x Pi ) + ˇ1 (D) + ˇ2 (A) + ˇ3 (RH) + ˇ4 (BD) + ˇ5 (CC) + ˇ6 (FC) + ˇ7 (BL) + ˇ8 (SH) + Eijkl Model 2: Rump height, body depth, chest circumference, flank circumference, navel height and body length Yijklmn = + Pi + ENj + BSk + RSl + BCSm + ˇ1 (D) + ˇ2 (A) + ˇ3 (RH) + ˇ4 (BD) + ˇ5 (CC) + ˇ6 (FC) + ˇ7 (BL) + ˇ8 (SH) + Eijklmn where: Yijklmn is the response variable (Total number of calves lost from calving to weaning for each cow, rump height, body depth, chest circumference, flank circumference, navel height and body length); the population mean common to all observations; Pi the effect of the ith parity of cow; ENj the effect of the jth production environment (sub-humid and semi-arid); BSk the effect of the kth breed score; RSl the effect of the lth reproductive status (early lactation; mid lactation; late lactation; early pregnancy; mid pregnancy and late pregnancy); BCSm the effect of the mth body condition score; BD × Pi the effect of the interaction between body depth and parity of the cow; ˇ1 –ˇ8 the partial linear regression coefficients of the dependent variables on covariates RH (rump height), BD (body depth), CC (chest circumference), FC (flank circumference), BD (body length), NH (navel height) respectively; Eijklm the residual error ∼ N (0; I 2 ). An ordinal logistic regression (PROC LOGISTIC) was used to estimate the probability of a cow experiencing a stillbirth, having an abortion and losing a calf from calving to weaning (SAS, 2008). The logit model-fitted predictors, production environment (sub-humid; semi-arid), age of cow (young cows; old cows) body depth, rump height, body length, flank circumference, chest circumference and navel height. The logit model used was: In[
P ] = ˇ0 + ˇ1 X1 + ˇ2 X2 . . . + ˇt Xt + ε 1−P
where: P is the probability of a cow (aborting; experiencing a stillbirth; losing a calf from calving to weaning); [P/1 − P] the odds ratio (the odds of a cow aborting; the odds of a cow having a stillbirth; the odds of a cow losing a calf from calving to weaning); ˇ0 the intercept; ˇ1 X1 ...ˇt Xt the regression coefficients of predictors; ε the random residual error. When computed for each predictor (ˇ1 ... ˇt ), the odds ratio was interpreted as the proportion of cows that abort versus those that did not abort, the proportion of cows that had stillbirths versus those that did not have any stillbirths and the proportion of cows that lost calves from calving to weaning versus those that did not lose any calf from calving to weaning. 3. Results 3.1. Summary statistics and levels of significance Summary statistics for the traits analysed are shown in Table 1. Table 2 shows the levels of significance for fixed effects and relevant covariates on, body depth, rump
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Table 1 Summary statistics for linear measurements, calving interval, weaning percentage, age of cow and body condition score (BCS) for animals used in the study. Variable
N
Mean
SD
Minimum
Maximum
Body depth (cm) Rump height (cm) Body length (cm) Flank circumference (cm) Chest circumference (cm) Navel height (cm) Calving interval (years) a TCL BCS Breed score
250 244 250 250 250 247 239 246 250 250
102.9 127.1 127.2 177.1 167.2 51.7 1.5 1 3.5 8
6.06 4.94 6.52 10.87 8.33 4.36 0.70 1.06 0.52 1.01
89 108 111 148 144 36 1 0 2.5 5
121 143 177 209 193 63 3 5 4.5 9
a
TCL = Total number of calves lost from calving to weaning for each cow.
Table 2 Means, root mean square errors (RMSE), R-squares (R2 ) and p-values for fixed effects and covariates tested for statistical models used to estimate the impact of rump height (RH), body depth, chest circumference (CC), flank circumference (FC), navel height (NH) and body length (BL) on reproductive efficiency of Nguni cows. a
Mean RMSE R2 Body depth (BD) Age of cow Production environment Breed score BCS b Reproductive status Parity Parity × BD
1 0.99 0.41 0.0001 0.3 0.13 0.47 − − 0.61 0.0006
BD
RH
BL
FC
CC
NH
102.93 4.97 0.56 − 0.82 0.0001 0.03 0.03 0.01 0.04 −
127.13 4.49 0.22 − 0.47 0.51 0.0001 0.90 0.71 0.39 −
127.22 5.04 0.31 − 0.46 0.78 0.0001 0.31 0.19 0.13 −
177.14 8.65 0.67 − 0.74 0.007 0.001 0.0001 0.18 0.07 −
167.19 6.85 0.65 − 0.06 0.003 0.05 0.0001 0.19 0.40 −
51.74 4.35 0.18 − 0.98 0.04 0.75 0.29 0.60 0.34 −
TCL = Total number of calves lost from calving to weaning for each cow. Reproductive status = pregnancy or lactation stage (early lactation; mid lactation; late lactation; early pregnancy; mid pregnancy and late pregnancy).
height, body length, flank circumference, chest circumference, navel height and TCL. 3.2. Effects of production environment, breed score, body condition and reproductive status of cow on linear traits The effects of production environment, breed score and reproductive status of cow on linear traits are shown in Table 3. The cows in semi-arid areas had deeper bodies, wider chests and flanks than those in sub-humid environments (p < 0.05). Cows in semi-arid areas had navels nearer to the ground than cows in sub-humid areas (p < 0.05). Cows with a breed score of nine were the shortest, with shallowest bodies, narrowest chests and flanks (p < 0.05). Pregnant cows had deeper bodies than lactating cows (p < 0.05). Body depth did not differ with pregnancy stage. The body depth increased (p < 0.05) with increase in BCS (Fig. 1). 3.3. Association of linear-type traits with calving interval, abortions, incidence of stillbirths and pre-weaning losses
decreased (p < 0.05) with an increase in parity up to Parity 5, then increased in Parity 6. The rate of decrease in TCL with increase in body depth was highest in Parity 2 (b = -0.06). There was no relationship between TCL and body depth in cows in Parity 4 (p > 0.05). Odds ratio estimates of cows calving every year, aborting, having a still birth and losing a calf from calving to
112 110 108
Body depth (cm)
a b
TCL
106 104 102 100 98
Significance levels, estimates and standard errors of the estimates for effects included in the regression models for relationship between body depth and TCL across parities are shown in Table 4. The TCL generally decreased with increase in body depth in all parities expect parity 4. The rate of decrease in TCL with increase in body depth
2
2.5
3
3.5
4
4.5
5
Body condition score Fig. 1. Association between body condition score and body depth (mean ± SE) in Nguni cows (N = 200).
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Table 3 Least square means (± se) (cm) for the effects of production environment, breed score and reproductive status on body depth (BD), rump height (RH), body length (BL), flank circumference (FC), chest circumference (CC) and navel height (NH) in Nguni cows. BD
RH
BL
FC
CC
NH
Production environment Semi-arid Sub-humid
104.8 ± 1.34a 100.7 ± 1.25b
128.1 ± 1.21 127.6 ± 1.13
129.1 ± 1.36 129.3 ± 1.27
179.2 ± 2.33a 175.3 ± 2.18b
171.6 ± 1.84a 168.1 ± 1.73b
50.7 ± 1.17a 52.3 ± 1.09b
Breed score 5 6 7 8 9
103.8 102.3 104.5 102.5 100.6
± ± ± ± ±
1.57b 1.76a,b 1.66b 1.28b 1.15a
127.4 127.8 129.0 129.7 125.6
± ± ± ± ±
2.33a 1.60a,b 1.50a,b 1.16b 1.04b
131.6 130.8 127.7 130.4 125.6
± ± ± ± ±
2.61b 1.79b 1.68a,b 1.30b 1.16a
174.0 184.0 176.6 178.1 173.4
± ± ± ± ±
4.48a,b 3.07c 2.88a,b 2.22b 2.00a
167.5 172.0 172.1 170.7 166.8
± ± ± ± ±
3.55 2.43 2.28 1.76 1.58
52.3 50.8 51.1 52.1 51.2
± ± ± ± ±
2.25 1.55 1.45 1.12 1.01
Reproductive status Early lactation Mid lactation Late lactation Early pregnancy Mid pregnancy Late pregnancy
105.0 102.1 102.4 104.3 103.2 106.1
± ± ± ± ± ±
1.35b 1.59a 1.39a 1.45a,b 1.63a,b 1.40b
128.9 128.8 128.2 127.3 127.1 127.5
± ± ± ± ± ±
1.22 1.44 1.26 1.32 1.48 2.27
129.1 130.5 128.7 129.4 126.1 129.9
± ± ± ± ± ±
1.37 1.61 1.41 1.48 1.62 1.42
180.7 177.6 177.7 176.4 175.8 180.6
± ± ± ± ± ±
2.35 2.76 2.42 2.53 2.76 2.43
171.9 168.4 168.4 169.9 167.8 171.8
± ± ± ± ± ±
1.86 2.19 1.92 2.00 2.25 1.93
51.3 50.7 52.0 51.2 50.9 49.9
± ± ± ± ± ±
1.18 1.39 1.22 1.27 1.45 1.23
Note: Values of the same parameter with different superscripts, within a column, are statistically different (p < 0.05). Table 4 Estimates (± SE) for the impact of body depth on total number of calves lost before weaning for each cow (TCL) in each parity. Parity
Intercept
2 3 4 5 6
6.4 4.9 1.83 1.15 3.2
± ± ± ± ±
TCL
1.63 2.11 2.37 3.58 3.39
-0.06 -0.04 -0.01 -0.01 -0.03
p-value ± ± ± ± ±
0.016 0.021 0.023 0.035 0.033
0.0008 0.04 0.68 0.006 0.04
weaning are shown in Table 5. For each unit increase in body depth, the odds of a cow aborting decreased by 1.12 and the odds of a cow having stillbirth decreased by 1.15. A unit increase in body depth resulted in the odds of a cow losing a calf from calving to weaning decreasing by 1.06. A unit change in body depth did not significantly influence the odds of a cow having a calving interval of 1 year (confidence interval 0.99−1.15). A unit change in body length, flank circumference, chest circumference and navel height did not significantly influence the odds of a cow having a calving interval of 1 year,
aborting, having stillbirths or losing a calf from calving to weaning. 3.4. Association of breed score, age of cow with production environment and calving interval, abortions, incidence of stillbirths and pre-weaning losses. Young cows were more likely to experience calving intervals greater than 1 year, stillbirths and abortions (Table 5). The odds of a calving interval of 1 year among cows in sub-humid areas were 2.57 times higher than the odds of calving interval of 1 year among cows in semiarid areas (Table 5). Cows in semi-arid regions were 2.13 times more likely to lose a calf from calving to weaning than cows in sub-humid areas. There was no significanct difference in the odds of aborting and stillbirths among cows in semi-arid regions and odds of aborting and stillbirth among cows in sub-humid areas (confidence interval 0.41−2.07 and 0.52−2.00, respectively). A unit change in breed score resulted in odds of a cow aborting and having stillbirths increasing by 1.37 and 1.10, respectively. For
Table 5 Odds ratio estimates, lower (LCI) and upper confidence (UCI) interval of cows calving every year, aborting, having a still birth and losing a calf from calving to weaning. a
Predictor
Odds
LCI
UCI
Odds
LCI
UCI
Odds
LCI
UCI
Mortality from birth to weaning Odds LCI UCI
Production environment (Sub-humid vs.Semi-arid) Age (young cows vs. old cows) Breed score Body depth Rump height Body length Flank circumference Chest circumference Navel height
2.57b
2.40
4.72
0.93c
0.41
2.07
1.02c
0.52
2.00
0.47b
0.24
0.90
0.98c 1.37b 1.07c 1.02c 1.01c 1.01c 0.98c 0.98c
0.77 0.55 0.99 0.95 0.95 0.97 0.93 0.91
1.98 0.97 1.15 1.11 1.07 1.06 1.03 1.06
0.78c 1.37b 0.89b 0.98c 1.03c 1.03c 0.96c 0.99c
0.83 1.02 0.81 0.88 0.97 0.97 0.89 0.89
1.99 2.03 0.98 1.08 1.09 1.09 1.03 1.10
0.97c 1.10b 0.87b 1.04c 1.00c 1.02c 1.00c 0.94c
0.55 1.01 0.80 0.96 0.95 0.97 0.95 0.86
1.91 1.48 0.95 1.14 1.05 1.07 1.07 1.03
1.17c 0.84c 0.94b 0.95c 1.05c 1.02c 1.02c 1.02c
0.64 0.63 0.78 0.87 0.99 0.97 0.96 0.93
2.15 1.10 0.92 1.03 1.11 1.07 1.08 1.11
a b c
Calving interval
Abortion
Still birth
Probability modelled is calving interval = 1 year; Odds ratios statistically significant; Odds ratios not statistically significant.
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each unit increase in breed score, the odds of a cow calving yearly increased by 1.37. 4. Discussion The mean calving interval of 1.5 years agrees with Nqeno et al. (2011). The mean body condition score of 3 was in line with findings by Muchenje et al. (2007). The finding that age of cow did not affect body length, rump height, navel height, body depth, flank circumference and chest circumference confirm findings by Zindove et al. (2015) who used similar age classes. Age of cow is expected to affect body size characteristics in cattle, as reported by Maiwashe et al. (2002). Morphological growth of animals goes alongside age. Linear characteristics of cows, however, vary less with increase in age (Yanar, 1999). Nguni cows used in this study might have reached their potential size and, hence, there was less morphological variation. Unexpectedly, there was no association of age of cow with calving interval, pre-weaning mortality and incidence of stillbirths or abortions. Age of cows is expected to influence pre-weaning mortality, incidence of still births and abortions (Akar and Yildiz, 2005; Schmidek et al., 2013). Our findings are difficult to explain. It could, however, be due to a few age group categories in the data. The effect of age of cow on the association between linear-type traits and reproductive performance needs to be further investigated using many age groups of cows. The high odds ratio estimate for the effect of production environment confirms results by Maciel et al. (2013a,b) who reported that calving interval of Nguni cows varied with geographical region. Differences in calving interval across production environment can be attributed to nutritional differences between the study areas. Poor nutrition and heat stress in semi-arid areas are the major cause of long calving intervals in semiarid regions (Ball and Peters, 2004). The semi-arid areas are subjected to frequent droughts when compared with sub-humid areas (Gusha et al., 2013). The finding that cows in semi-arid region had deeper bodies, wider flanks and chests than those in sub-humid areas could be a result of differences in rainfall patterns, temperature, veld type and mineral status of the soil. This is in line with arguments put forward by Maciel et al. (2013a,b) that Nguni cattle kept under different environments will evolve into different ecotypes in the long run as a result of the interaction between the environmental factors and their individual genetic capacities. Semi-arid regions are characterised by scanty rainfall and scrubby vegetation (Gusha et al., 2013). It has been suggested that body depth, flank circumference and chest circumference all determine body capacity in cows (Zindove et al., 2015). Deep bodies, wide flanks and chests for cows in semi-arid areas could be an adaptation to provide large body capacity hence lots of room to consume and digest large amounts of high-fibre; lower protein feeds to meet the cows’ nutritional requirements. The results that increase in breed score resulted in increase in chances of a cow aborting or having stillbirths can be due to the decrease in body depth as breed score increased. This maybe because body depth limits gut size (Hansen et al., 1999) and, thus, cows with shallow bodies are more likely to consume less thereby struggling to meet
nutritional requirements during pregnancy when fed on natural pastures of poor nutritional value. The high and significant odds ratio estimates for the effect of body depth on abortion and stillbirths can be attributed to the relationship between of body depth and nutrition of the cow. Body depth is a component trait of body capacity hence it affects nutrition of the cow (Wu et al., 2013). Faulty nutrition during gestation is one of the nutritional reasons for stillbirths and abortions (Khodakaram-Tafti and Ikede, 2005). Nguni cattle owned by resource-poor farmers are kept on communal rangelands, which are of low-energy, high-fibre and poor digestibility (Nqeno et al., 2011). Inorder to meet their energy requirements, cows on less-digestible, low-energy, high-fibre pastures needs to consume large amounts of dry matter. Consumption of less-digestible, low-energy, high-fibre diets is controlled by rumen fill and the feed passage rate through the gastrointestinal tract (Hill, 2012). As the body depth increases, the body and gut capacity also increases hence passage rates are longer (Hansen et al., 1999). As are result of increased body and gut capacity, dry matter intake and rate of nutrient absorption potentially increases. Thus, under less-digestible, low-energy and high-fibre pastures, cows with deeper bodies are more likely to meet their nutritional requirements compared with those with shallow bodies. Pregnant cows with shallow bodies, hence low rumen fill, may struggle to ingest adequate amounts of dietary energy, vitamins and other nutrients to meet the requirements of the foetuses resulting in abortions or stillbirths. Considering that most communal Nguni farmers are resource poor and cannot afford to supplement nutritional requirements to cows during pregnancy (Mapiye et al., 2009), it can be recommended that they resort to selecting cows with deeper bodies to overcome abortions and stillbirths in their herds. There is, however, need to ascertain how much of the variation in stillbirths and abortions is associated with body depth considering that there are many other factors that affect incidence of stillbirths and abortion, such as diseases and genetic abnormalities. The observed decrease in the rate of decrease in total number of calves lost before weaning with increase in body depth across parities can be explained by variations in nutrient requirements of cows in different parities. Cows have biological priority for nutrients with maintenance coming first, followed by own growth, lactation, foetal growth, reserves then breeding (Short et al., 1990). Since first calvers will still be growing, they compete with their foetuses for available nutrients for their growth and maintenance during pregnancy. They also have to partition their dietary energy between milk production, growth and maintenance during lactation period. Pregnant or lactating young cows with deeper bodies, hence long passage rates, large body and gut capacity are capable of consuming large amounts of dry matter and digest thoroughly. That is they can meet their nutritional requirements as well as nutritional requirements of the foetus. Pregnant young cows with shallow bodies, hence short passage rates, small body and gut capacity, may struggle to consume amounts of dry matter enough to meet their high nutritional requirements resulting in birth of weak calves. Younger cows have more
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critical nutritional needs (Mulliniks et al., 2012) and this could explain why the rate of decrease in total number of calves lost before weaning with increase in body depth is more pronounced in early parities. The finding that production environment did not influence the incidence of abortion and stillbirth in cows is unexpected. Semi-arid areas have characterised by erratic rainfall, predominated by aloes, thorn bush, some hardwood and the areas are prone to droughts (Gusha et al., 2013). Cows in semi-arid areas expected to be more likely to abort or have stillbirths due to lake of adequate nutrients coupled with frequent extreme temperatures. Sub-humid areas are characterised by bushes, woodlands and grasslands (Morgenthal et al., 2006). Nguni cows kept in sub-humid areas are expected to be less likely to abort or have stillbirths due to the availability of quality feed and adequate nutrients. Since cows with deeper bodies are capable of consuming large amounts of dry matter and digest thoroughly, the finding that cows in the semiarid regions had deeper bodies than those in sub-humid areas could be the reason why production environment did not influence the incidence of lost pregnancy and stillbirth in cows. Cows in semi-arid areas were more likely to lose calves from birth to weaning than those in sub-humid areas probably because of large temperature fluctuations. Although there is limited, if any, scientific knowledge on the effect of climatic conditions on mortality in Nguni calves in communal production, persistent extremely high temperatures have been associated with an increased risk of beef calf mortality in general (Mapekula et al., 2009).
5. Conclusions Production environment affected body depth, flank circumference, chest circumference and navel height, calving interval and mortality of calves from birth to weaning. Low nutritional levels, coupled with extreme climatic conditions may have resulted in cows raised in semi-arid areas being more likely to have longer calving intervals (more than 1 year) and lose calves during the period between calving and weaning. Body depth had a significant influence on incidence of stillbirths and abortions but not mortality of calves from birth to weaning. As body depth increased, total number of calves lost by a cow from calving to weaning decreased linearly. The rate of decrease in number of calves lost by a cow as body depth increased decreased with increase in parity. Thus, the selection of cow with deep bodies could possibly lead to increased fertility in communal Nguni production. There is, however, need for further analysis on whether the association between linear traits and calving interval, abortions, incidence of stillbirths and pre-weaning losses differ with age using many age groups of cows. This could be a starting point to incorporating linear traits and/or visual appraisal for fertility improvement programmes for beef cattle under extensive production.
Conflict of interest statement Authors have no conflict of interest.
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Are calving interval, abortions, incidence of stillbirths and pre-weaning losses in Nguni cows associated with linear type traits? T.J. Zindove, M. Chimonyo ∗ Animal and Poultry Science, School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, P. Bag X01, Scottsville 3209, Pietermaritzburg, South Africa
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Article history: Received 10 December 2014 Received in revised form 15 June 2015 Accepted 16 July 2015 Available online xxx Keywords: Nguni cows Body depth Calving interval Flank circumference Chest circumference
a b s t r a c t The association of six linear type traits with calving interval, abortions, incidence of stillbirths and pre-weaning losses in Nguni cows in semi-arid and sub-humid communal areas was investigated. It was hypothesised that the odds of a cow having caving interval greater than 1 year, aborting, experiencing stillbirths or losing a calf from calving to weaning decreased with increase in body depth, rump height, flank circumference, chest circumference, navel height and body length. Navel height was measured as the distance from the ground to the lowest point of the cow’s belly bottom (navel). Data were collected from a total of 200 Nguni cows from two sites experiencing sub-humid and semi-arid environments (100 each) between May and June 2013. Cows in sub-humid regions were 2.57 times more likely to have a calving interval of 1 year than cows in semi-arid areas. As body depth increased, the number of calves lost by a cow before weaning decreased linearly (p < 0.05) in all parities except parity 4. Cows in semi-arid regions were 2.13 times more likely to lose a calf from calving to weaning. For each unit increase in body depth, the odds of a cow aborting decreased by 1.12 and the odds of a cow having stillbirth decreased by 1.15. Rump height, flank circumference, chest circumference, navel height and body length were not associated with calving interval, abortions, incidence of stillbirths and pre-weaning losses. It was, therefore, concluded that body depth influences calving interval, incidence of stillbirths and abortions in Nguni cows. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Poor reproductive performance, a challenge of cattle production in rural communal farming systems, has been attributed to low levels of management (Mashoko et al., 2007). Infertility, abortions, stillbirths and high calf mortality rates from birth to weaning are main reproduction constraints to cattle production in communal areas (Mokantla et al., 2004). Low calving percentage can be
∗ Corresponding author. E-mail address: [email protected] (M. Chimonyo).
a result of cows failing to conceive and/or foetal losses (abortions and stillbirths). Stillbirths and abortions have been attributed to various factors including high disease prevalence and poor nutrition (Khodakaram-Tafti and Ikede, 2005). Calving percentages vary yearly due to environmental stresses, such as droughts and fluctuation of environmental temperatures (Gusha et al., 2013); suggesting nutrition and environmental stress play critical roles. In South Africa, the recent quest for viable breeds in communal production systems has resulted in the reintroduction the Nguni breed, a low maintenance breed suitable for low-input systems based on extensive grazing
http://dx.doi.org/10.1016/j.anireprosci.2015.07.002 0378-4320/© 2015 Elsevier B.V. All rights reserved.
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(Bester et al., 2003). The Nguni, a small to medium-framed breed, is extremely hardy and well adapted to harsh environmental conditions of the Southern Sahara. Nguni cattles are resistant to diseases and gastrointestinal parasites, which are among the major causes of low reproductive efficiency in communal cattle production (Ndlovu et al., 2009). Due their adaptation to low quality feeds, Nguni cows have the potential to exhibit high fertility characteristics, such high conception rates, early maturing and short calving intervals. Despite their huge production potential, offtake of Nguni in communal production systems has not yet reached acceptable levels (Musemwa et al., 2010). Low off-take for communal Nguni farmers has been largely attributed to low reproductive efficiency as a result of poor breeding practices, such as poor selection and uncontrolled mating systems (Mapiye et al., 2009). Nqeno et al. (2011) reported that, in South African communal production systems, 65% of farmers have Nguni herds with average calving intervals of 2 years, whilst 55% have cows which experience stillbirths or abortions. Under communal farming systems, calving occur throughout the year. Records are hardly kept and selection of the best individuals is difficult to perform. Communal Nguni farmers rely mostly on memory when selecting breeding cows and/or heifers. They have indigenous knowledge to memorise and acknowledge individual animal and ancestors’ performance (Mgongo et al., 2014). Information on livestock can, however, only be memorised up to a point and can often be forgotten overtime especially when herd composition drastically changes in cases such as drought, disease epidemics and other natural disasters. Considering that written records in communal cattle production are rare and, that memory based selection is not reliable, there is need to come up with complementary strategies to select for reproductive efficiency. Communal farmers use linear traits to complement memory-based selection during selective breeding of cows (Mapiye et al., 2009). High calf mortality rates from birth to weaning of about 30% per annum and long calving intervals of 2 years were, however, estimated in the communal production systems (Nqeno et al., 2011; Nowers et al., 2013). This can be because there is no evidence on the relationship between linear traits and reproductive performance in small-framed beef breeds. In dairy cows, there is a general relationship between the linear traits and reproductive performance (Larroque and Ducrocq, 2001). If the relationship between linear and reproductive efficiency is ascertained, farmers can select breeding cows with ease through visual appraisal. Visual appraisal using linear traits will be cheaper for the poor resource farmers. The objective of the study was to determine whether caving interval, incidence of abortions, incidence of stillbirths and calf mortality in multiparous Nguni cows are associated with linear-type traits. 2. Materials and methods 2.1. Study site The study was conducted in Jozini local municipality, representing sub-humid production environment and
Msinga local municipality representing semi-arid production environment. Both sites are in KwaZulu-Natal province of South Africa. Jozini is located at 27◦ 25 60 S, 32◦ 4 0 E. The altitude is between 150 and 600 m above sea level. The climate is characterised by hot-dry and cool-wet seasons. Annual rainfall averages 600 mm. Most rains are received between January and March, with the months of June and July being dry and cool. Highest mean monthly temperature is recorded in January (30 ◦ C) and lowest in July (11 ◦ C). The vegetation type of the area is mainly coastal sand veld, bush veld and foothill wooded grasslands (Morgenthal et al., 2006). Msinga is located at 28◦ 74 61 S, 30◦ 45 25 E. It receives erratic rainfall and has large daily temperature ranges. The area experiences extremely hot summers with highest mean monthly maximum temperature of 37 ◦ C in January. There is severe cold with frost, with mean monthly minimum temperatures ranging between 4 and 8 ◦ C between May and July. The vegetation type is semi-arid savannah with steep and stony mountains predominated by aloes, thorn bush and some hardwood. 2.2. Data collection A total of 200 multiparous cows were used. Twenty farmers (10 from each region) with at least 10 multiparous Nguni cows in their herd were selected using the snowball technique. The cows were selected on the basis of the owners’ willingness to participate in the study. The cattle grazed on communal rangelands. Measurements were taken during dipping days between May and June 2013. Just before dipping, cattle were held in a race for measurement. A trained person identified 10 Nguni cows from each of the selected farmers’ herds (five young cows and five old cows). The age of the cow was determined by dentition. Cows were divided into two age groups, young (7 years and below)—with visible incisors and old (8 years and above)—with broken or gummy mouth (Raines et al., 2008). The breed score and body condition score (BCS) of the cows were then determined. Visual assessment of the body condition was made using the five-point European system, where a score of 1 is emaciated, and a score of 5 is very fat (Edmonson et al., 1989). Before taking the measurements, each farmer was interviewed on number of calvings (parity of cow), average calving interval (CI), when the cow last calved, when they noticed the cow was pregnant (for pregnant cows), number of stillbirths, when the cow had its last stillbirth, number of abortions, when the cow had its last abortion, number of calves that died before weaning (9 months) and number of calves weaned. Stillbirth was defined as death of a calf at birth or within 24 h of birth after approximately 8 months of gestation or more (Berglund et al., 2003). A cow was considered to have aborted if it gave birth to a dead foetus before 8 months of gestation (Trees et al., 1999). The CI was recorded for cows in parity 3 and above. Reproductive status for each cow was categorised into early pregnancy (less than 3 months), mid pregnancy (4−6 months), late pregnancy (7−9 months), early lactation (less than 3 months), mid lactation (4−6 months) and late lactation (more than 7 months). Interviews were conducted in Zulu vernacular by a trained enumerator. Stillbirths, abortions and calves lost from
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calving to weaning were coded as categorical traits (1 = had stillbirth, 0 = did not have stillbirth; 1 = had an abortion, 0 = did not have an abortion; 1 lost a calf from calving to weaning; 0 = no calf died before weaning). Measurements were taken between 07.00 and 10.00 h before cows had started grazing. Records were taken once from each cow. The measurements taken were rump height, body depth, chest circumference, flank circumference, navel height and body length. The rump height was measured from top of the spine in between hips to the ground. Body depth was measured as distance between the top of spine and bottom of barrel at last rib (the deepest point) measured from the left side of the cow. Chest circumference was defined as circumference of the body taken just behind the shoulders. Flank circumference was defined as circumference of the body taken just in front of the hook bones. Navel height was measured as the distance from the ground to the lowest point of the cow’s belly bottom (navel). Body length was measured from the hindmost part of the animal to the valley in front of the second thoracic vertebrae just ahead of the centre of the shoulders (Alphonsus et al., 2012). Body depth, chest circumference, body length and flank circumference were measured using a plastic tape measure. Navel height and rump height were measured using an aluminium extending measuring stick obtained from Scales 2000 Ltd, Westville, South Africa. To ensure consistency, all measurements were taken by the same individual. Breed scores were assessed visually by the same assessor throughout the experimental period. Each animal was scored using a 1−9 scale based on nine physical characteristics of Nguni cows as described by Nguni breeders association. Each cow would be given a score corresponding to the number of descriptive characteristics it possessed. Physical characteristics considered were: 1: general size of small to medium (rump height less than 130 cm), 2: less developed dewlap and umbilical fold, 3: hardly noticeable cervico-thoracic hump, 4: rump drooping towards tail, 5: moderately dipped forehead constricted just below the horns, 6: wide and slightly convex face, 7: small ears with a sharp apex, 8: small udders and teats, 9: noticeably lyre-shaped horns. A cow was considered for this study only if it met at least five of the nine physical characteristics. A score of five means the cow met five of the nine physical characteristics and a score of nine means that the cow met all the nine characteristics.
2.3. Statistical analyses The effects of production environment and parity of cow on linear traits and total number of calves lost from calving to weaning for each cow (TCL) were analysed using the General Linear Model procedures (SAS, 2008), assuming fixed models with all possible first-, second- and thirdorder interactions. Models for final analyses were obtained after eliminating interactions that were not significant (p > 0.05). The body depth, flank circumference, chest circumference, body length, navel height and rump height were fitted as covariates where relevant. The following models were used:
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Model 1: Total number of calves lost before weaning for each cow Yijkl = + Pi + ENj + BSk + (BD x Pi ) + ˇ1 (D) + ˇ2 (A) + ˇ3 (RH) + ˇ4 (BD) + ˇ5 (CC) + ˇ6 (FC) + ˇ7 (BL) + ˇ8 (SH) + Eijkl Model 2: Rump height, body depth, chest circumference, flank circumference, navel height and body length Yijklmn = + Pi + ENj + BSk + RSl + BCSm + ˇ1 (D) + ˇ2 (A) + ˇ3 (RH) + ˇ4 (BD) + ˇ5 (CC) + ˇ6 (FC) + ˇ7 (BL) + ˇ8 (SH) + Eijklmn where: Yijklmn is the response variable (Total number of calves lost from calving to weaning for each cow, rump height, body depth, chest circumference, flank circumference, navel height and body length); the population mean common to all observations; Pi the effect of the ith parity of cow; ENj the effect of the jth production environment (sub-humid and semi-arid); BSk the effect of the kth breed score; RSl the effect of the lth reproductive status (early lactation; mid lactation; late lactation; early pregnancy; mid pregnancy and late pregnancy); BCSm the effect of the mth body condition score; BD × Pi the effect of the interaction between body depth and parity of the cow; ˇ1 –ˇ8 the partial linear regression coefficients of the dependent variables on covariates RH (rump height), BD (body depth), CC (chest circumference), FC (flank circumference), BD (body length), NH (navel height) respectively; Eijklm the residual error ∼ N (0; I 2 ). An ordinal logistic regression (PROC LOGISTIC) was used to estimate the probability of a cow experiencing a stillbirth, having an abortion and losing a calf from calving to weaning (SAS, 2008). The logit model-fitted predictors, production environment (sub-humid; semi-arid), age of cow (young cows; old cows) body depth, rump height, body length, flank circumference, chest circumference and navel height. The logit model used was: In[
P ] = ˇ0 + ˇ1 X1 + ˇ2 X2 . . . + ˇt Xt + ε 1−P
where: P is the probability of a cow (aborting; experiencing a stillbirth; losing a calf from calving to weaning); [P/1 − P] the odds ratio (the odds of a cow aborting; the odds of a cow having a stillbirth; the odds of a cow losing a calf from calving to weaning); ˇ0 the intercept; ˇ1 X1 ...ˇt Xt the regression coefficients of predictors; ε the random residual error. When computed for each predictor (ˇ1 ... ˇt ), the odds ratio was interpreted as the proportion of cows that abort versus those that did not abort, the proportion of cows that had stillbirths versus those that did not have any stillbirths and the proportion of cows that lost calves from calving to weaning versus those that did not lose any calf from calving to weaning. 3. Results 3.1. Summary statistics and levels of significance Summary statistics for the traits analysed are shown in Table 1. Table 2 shows the levels of significance for fixed effects and relevant covariates on, body depth, rump
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Table 1 Summary statistics for linear measurements, calving interval, weaning percentage, age of cow and body condition score (BCS) for animals used in the study. Variable
N
Mean
SD
Minimum
Maximum
Body depth (cm) Rump height (cm) Body length (cm) Flank circumference (cm) Chest circumference (cm) Navel height (cm) Calving interval (years) a TCL BCS Breed score
250 244 250 250 250 247 239 246 250 250
102.9 127.1 127.2 177.1 167.2 51.7 1.5 1 3.5 8
6.06 4.94 6.52 10.87 8.33 4.36 0.70 1.06 0.52 1.01
89 108 111 148 144 36 1 0 2.5 5
121 143 177 209 193 63 3 5 4.5 9
a
TCL = Total number of calves lost from calving to weaning for each cow.
Table 2 Means, root mean square errors (RMSE), R-squares (R2 ) and p-values for fixed effects and covariates tested for statistical models used to estimate the impact of rump height (RH), body depth, chest circumference (CC), flank circumference (FC), navel height (NH) and body length (BL) on reproductive efficiency of Nguni cows. a
Mean RMSE R2 Body depth (BD) Age of cow Production environment Breed score BCS b Reproductive status Parity Parity × BD
1 0.99 0.41 0.0001 0.3 0.13 0.47 − − 0.61 0.0006
BD
RH
BL
FC
CC
NH
102.93 4.97 0.56 − 0.82 0.0001 0.03 0.03 0.01 0.04 −
127.13 4.49 0.22 − 0.47 0.51 0.0001 0.90 0.71 0.39 −
127.22 5.04 0.31 − 0.46 0.78 0.0001 0.31 0.19 0.13 −
177.14 8.65 0.67 − 0.74 0.007 0.001 0.0001 0.18 0.07 −
167.19 6.85 0.65 − 0.06 0.003 0.05 0.0001 0.19 0.40 −
51.74 4.35 0.18 − 0.98 0.04 0.75 0.29 0.60 0.34 −
TCL = Total number of calves lost from calving to weaning for each cow. Reproductive status = pregnancy or lactation stage (early lactation; mid lactation; late lactation; early pregnancy; mid pregnancy and late pregnancy).
height, body length, flank circumference, chest circumference, navel height and TCL. 3.2. Effects of production environment, breed score, body condition and reproductive status of cow on linear traits The effects of production environment, breed score and reproductive status of cow on linear traits are shown in Table 3. The cows in semi-arid areas had deeper bodies, wider chests and flanks than those in sub-humid environments (p < 0.05). Cows in semi-arid areas had navels nearer to the ground than cows in sub-humid areas (p < 0.05). Cows with a breed score of nine were the shortest, with shallowest bodies, narrowest chests and flanks (p < 0.05). Pregnant cows had deeper bodies than lactating cows (p < 0.05). Body depth did not differ with pregnancy stage. The body depth increased (p < 0.05) with increase in BCS (Fig. 1). 3.3. Association of linear-type traits with calving interval, abortions, incidence of stillbirths and pre-weaning losses
decreased (p < 0.05) with an increase in parity up to Parity 5, then increased in Parity 6. The rate of decrease in TCL with increase in body depth was highest in Parity 2 (b = -0.06). There was no relationship between TCL and body depth in cows in Parity 4 (p > 0.05). Odds ratio estimates of cows calving every year, aborting, having a still birth and losing a calf from calving to
112 110 108
Body depth (cm)
a b
TCL
106 104 102 100 98
Significance levels, estimates and standard errors of the estimates for effects included in the regression models for relationship between body depth and TCL across parities are shown in Table 4. The TCL generally decreased with increase in body depth in all parities expect parity 4. The rate of decrease in TCL with increase in body depth
2
2.5
3
3.5
4
4.5
5
Body condition score Fig. 1. Association between body condition score and body depth (mean ± SE) in Nguni cows (N = 200).
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Table 3 Least square means (± se) (cm) for the effects of production environment, breed score and reproductive status on body depth (BD), rump height (RH), body length (BL), flank circumference (FC), chest circumference (CC) and navel height (NH) in Nguni cows. BD
RH
BL
FC
CC
NH
Production environment Semi-arid Sub-humid
104.8 ± 1.34a 100.7 ± 1.25b
128.1 ± 1.21 127.6 ± 1.13
129.1 ± 1.36 129.3 ± 1.27
179.2 ± 2.33a 175.3 ± 2.18b
171.6 ± 1.84a 168.1 ± 1.73b
50.7 ± 1.17a 52.3 ± 1.09b
Breed score 5 6 7 8 9
103.8 102.3 104.5 102.5 100.6
± ± ± ± ±
1.57b 1.76a,b 1.66b 1.28b 1.15a
127.4 127.8 129.0 129.7 125.6
± ± ± ± ±
2.33a 1.60a,b 1.50a,b 1.16b 1.04b
131.6 130.8 127.7 130.4 125.6
± ± ± ± ±
2.61b 1.79b 1.68a,b 1.30b 1.16a
174.0 184.0 176.6 178.1 173.4
± ± ± ± ±
4.48a,b 3.07c 2.88a,b 2.22b 2.00a
167.5 172.0 172.1 170.7 166.8
± ± ± ± ±
3.55 2.43 2.28 1.76 1.58
52.3 50.8 51.1 52.1 51.2
± ± ± ± ±
2.25 1.55 1.45 1.12 1.01
Reproductive status Early lactation Mid lactation Late lactation Early pregnancy Mid pregnancy Late pregnancy
105.0 102.1 102.4 104.3 103.2 106.1
± ± ± ± ± ±
1.35b 1.59a 1.39a 1.45a,b 1.63a,b 1.40b
128.9 128.8 128.2 127.3 127.1 127.5
± ± ± ± ± ±
1.22 1.44 1.26 1.32 1.48 2.27
129.1 130.5 128.7 129.4 126.1 129.9
± ± ± ± ± ±
1.37 1.61 1.41 1.48 1.62 1.42
180.7 177.6 177.7 176.4 175.8 180.6
± ± ± ± ± ±
2.35 2.76 2.42 2.53 2.76 2.43
171.9 168.4 168.4 169.9 167.8 171.8
± ± ± ± ± ±
1.86 2.19 1.92 2.00 2.25 1.93
51.3 50.7 52.0 51.2 50.9 49.9
± ± ± ± ± ±
1.18 1.39 1.22 1.27 1.45 1.23
Note: Values of the same parameter with different superscripts, within a column, are statistically different (p < 0.05). Table 4 Estimates (± SE) for the impact of body depth on total number of calves lost before weaning for each cow (TCL) in each parity. Parity
Intercept
2 3 4 5 6
6.4 4.9 1.83 1.15 3.2
± ± ± ± ±
TCL
1.63 2.11 2.37 3.58 3.39
-0.06 -0.04 -0.01 -0.01 -0.03
p-value ± ± ± ± ±
0.016 0.021 0.023 0.035 0.033
0.0008 0.04 0.68 0.006 0.04
weaning are shown in Table 5. For each unit increase in body depth, the odds of a cow aborting decreased by 1.12 and the odds of a cow having stillbirth decreased by 1.15. A unit increase in body depth resulted in the odds of a cow losing a calf from calving to weaning decreasing by 1.06. A unit change in body depth did not significantly influence the odds of a cow having a calving interval of 1 year (confidence interval 0.99−1.15). A unit change in body length, flank circumference, chest circumference and navel height did not significantly influence the odds of a cow having a calving interval of 1 year,
aborting, having stillbirths or losing a calf from calving to weaning. 3.4. Association of breed score, age of cow with production environment and calving interval, abortions, incidence of stillbirths and pre-weaning losses. Young cows were more likely to experience calving intervals greater than 1 year, stillbirths and abortions (Table 5). The odds of a calving interval of 1 year among cows in sub-humid areas were 2.57 times higher than the odds of calving interval of 1 year among cows in semiarid areas (Table 5). Cows in semi-arid regions were 2.13 times more likely to lose a calf from calving to weaning than cows in sub-humid areas. There was no significanct difference in the odds of aborting and stillbirths among cows in semi-arid regions and odds of aborting and stillbirth among cows in sub-humid areas (confidence interval 0.41−2.07 and 0.52−2.00, respectively). A unit change in breed score resulted in odds of a cow aborting and having stillbirths increasing by 1.37 and 1.10, respectively. For
Table 5 Odds ratio estimates, lower (LCI) and upper confidence (UCI) interval of cows calving every year, aborting, having a still birth and losing a calf from calving to weaning. a
Predictor
Odds
LCI
UCI
Odds
LCI
UCI
Odds
LCI
UCI
Mortality from birth to weaning Odds LCI UCI
Production environment (Sub-humid vs.Semi-arid) Age (young cows vs. old cows) Breed score Body depth Rump height Body length Flank circumference Chest circumference Navel height
2.57b
2.40
4.72
0.93c
0.41
2.07
1.02c
0.52
2.00
0.47b
0.24
0.90
0.98c 1.37b 1.07c 1.02c 1.01c 1.01c 0.98c 0.98c
0.77 0.55 0.99 0.95 0.95 0.97 0.93 0.91
1.98 0.97 1.15 1.11 1.07 1.06 1.03 1.06
0.78c 1.37b 0.89b 0.98c 1.03c 1.03c 0.96c 0.99c
0.83 1.02 0.81 0.88 0.97 0.97 0.89 0.89
1.99 2.03 0.98 1.08 1.09 1.09 1.03 1.10
0.97c 1.10b 0.87b 1.04c 1.00c 1.02c 1.00c 0.94c
0.55 1.01 0.80 0.96 0.95 0.97 0.95 0.86
1.91 1.48 0.95 1.14 1.05 1.07 1.07 1.03
1.17c 0.84c 0.94b 0.95c 1.05c 1.02c 1.02c 1.02c
0.64 0.63 0.78 0.87 0.99 0.97 0.96 0.93
2.15 1.10 0.92 1.03 1.11 1.07 1.08 1.11
a b c
Calving interval
Abortion
Still birth
Probability modelled is calving interval = 1 year; Odds ratios statistically significant; Odds ratios not statistically significant.
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each unit increase in breed score, the odds of a cow calving yearly increased by 1.37. 4. Discussion The mean calving interval of 1.5 years agrees with Nqeno et al. (2011). The mean body condition score of 3 was in line with findings by Muchenje et al. (2007). The finding that age of cow did not affect body length, rump height, navel height, body depth, flank circumference and chest circumference confirm findings by Zindove et al. (2015) who used similar age classes. Age of cow is expected to affect body size characteristics in cattle, as reported by Maiwashe et al. (2002). Morphological growth of animals goes alongside age. Linear characteristics of cows, however, vary less with increase in age (Yanar, 1999). Nguni cows used in this study might have reached their potential size and, hence, there was less morphological variation. Unexpectedly, there was no association of age of cow with calving interval, pre-weaning mortality and incidence of stillbirths or abortions. Age of cows is expected to influence pre-weaning mortality, incidence of still births and abortions (Akar and Yildiz, 2005; Schmidek et al., 2013). Our findings are difficult to explain. It could, however, be due to a few age group categories in the data. The effect of age of cow on the association between linear-type traits and reproductive performance needs to be further investigated using many age groups of cows. The high odds ratio estimate for the effect of production environment confirms results by Maciel et al. (2013a,b) who reported that calving interval of Nguni cows varied with geographical region. Differences in calving interval across production environment can be attributed to nutritional differences between the study areas. Poor nutrition and heat stress in semi-arid areas are the major cause of long calving intervals in semiarid regions (Ball and Peters, 2004). The semi-arid areas are subjected to frequent droughts when compared with sub-humid areas (Gusha et al., 2013). The finding that cows in semi-arid region had deeper bodies, wider flanks and chests than those in sub-humid areas could be a result of differences in rainfall patterns, temperature, veld type and mineral status of the soil. This is in line with arguments put forward by Maciel et al. (2013a,b) that Nguni cattle kept under different environments will evolve into different ecotypes in the long run as a result of the interaction between the environmental factors and their individual genetic capacities. Semi-arid regions are characterised by scanty rainfall and scrubby vegetation (Gusha et al., 2013). It has been suggested that body depth, flank circumference and chest circumference all determine body capacity in cows (Zindove et al., 2015). Deep bodies, wide flanks and chests for cows in semi-arid areas could be an adaptation to provide large body capacity hence lots of room to consume and digest large amounts of high-fibre; lower protein feeds to meet the cows’ nutritional requirements. The results that increase in breed score resulted in increase in chances of a cow aborting or having stillbirths can be due to the decrease in body depth as breed score increased. This maybe because body depth limits gut size (Hansen et al., 1999) and, thus, cows with shallow bodies are more likely to consume less thereby struggling to meet
nutritional requirements during pregnancy when fed on natural pastures of poor nutritional value. The high and significant odds ratio estimates for the effect of body depth on abortion and stillbirths can be attributed to the relationship between of body depth and nutrition of the cow. Body depth is a component trait of body capacity hence it affects nutrition of the cow (Wu et al., 2013). Faulty nutrition during gestation is one of the nutritional reasons for stillbirths and abortions (Khodakaram-Tafti and Ikede, 2005). Nguni cattle owned by resource-poor farmers are kept on communal rangelands, which are of low-energy, high-fibre and poor digestibility (Nqeno et al., 2011). Inorder to meet their energy requirements, cows on less-digestible, low-energy, high-fibre pastures needs to consume large amounts of dry matter. Consumption of less-digestible, low-energy, high-fibre diets is controlled by rumen fill and the feed passage rate through the gastrointestinal tract (Hill, 2012). As the body depth increases, the body and gut capacity also increases hence passage rates are longer (Hansen et al., 1999). As are result of increased body and gut capacity, dry matter intake and rate of nutrient absorption potentially increases. Thus, under less-digestible, low-energy and high-fibre pastures, cows with deeper bodies are more likely to meet their nutritional requirements compared with those with shallow bodies. Pregnant cows with shallow bodies, hence low rumen fill, may struggle to ingest adequate amounts of dietary energy, vitamins and other nutrients to meet the requirements of the foetuses resulting in abortions or stillbirths. Considering that most communal Nguni farmers are resource poor and cannot afford to supplement nutritional requirements to cows during pregnancy (Mapiye et al., 2009), it can be recommended that they resort to selecting cows with deeper bodies to overcome abortions and stillbirths in their herds. There is, however, need to ascertain how much of the variation in stillbirths and abortions is associated with body depth considering that there are many other factors that affect incidence of stillbirths and abortion, such as diseases and genetic abnormalities. The observed decrease in the rate of decrease in total number of calves lost before weaning with increase in body depth across parities can be explained by variations in nutrient requirements of cows in different parities. Cows have biological priority for nutrients with maintenance coming first, followed by own growth, lactation, foetal growth, reserves then breeding (Short et al., 1990). Since first calvers will still be growing, they compete with their foetuses for available nutrients for their growth and maintenance during pregnancy. They also have to partition their dietary energy between milk production, growth and maintenance during lactation period. Pregnant or lactating young cows with deeper bodies, hence long passage rates, large body and gut capacity are capable of consuming large amounts of dry matter and digest thoroughly. That is they can meet their nutritional requirements as well as nutritional requirements of the foetus. Pregnant young cows with shallow bodies, hence short passage rates, small body and gut capacity, may struggle to consume amounts of dry matter enough to meet their high nutritional requirements resulting in birth of weak calves. Younger cows have more
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critical nutritional needs (Mulliniks et al., 2012) and this could explain why the rate of decrease in total number of calves lost before weaning with increase in body depth is more pronounced in early parities. The finding that production environment did not influence the incidence of abortion and stillbirth in cows is unexpected. Semi-arid areas have characterised by erratic rainfall, predominated by aloes, thorn bush, some hardwood and the areas are prone to droughts (Gusha et al., 2013). Cows in semi-arid areas expected to be more likely to abort or have stillbirths due to lake of adequate nutrients coupled with frequent extreme temperatures. Sub-humid areas are characterised by bushes, woodlands and grasslands (Morgenthal et al., 2006). Nguni cows kept in sub-humid areas are expected to be less likely to abort or have stillbirths due to the availability of quality feed and adequate nutrients. Since cows with deeper bodies are capable of consuming large amounts of dry matter and digest thoroughly, the finding that cows in the semiarid regions had deeper bodies than those in sub-humid areas could be the reason why production environment did not influence the incidence of lost pregnancy and stillbirth in cows. Cows in semi-arid areas were more likely to lose calves from birth to weaning than those in sub-humid areas probably because of large temperature fluctuations. Although there is limited, if any, scientific knowledge on the effect of climatic conditions on mortality in Nguni calves in communal production, persistent extremely high temperatures have been associated with an increased risk of beef calf mortality in general (Mapekula et al., 2009).
5. Conclusions Production environment affected body depth, flank circumference, chest circumference and navel height, calving interval and mortality of calves from birth to weaning. Low nutritional levels, coupled with extreme climatic conditions may have resulted in cows raised in semi-arid areas being more likely to have longer calving intervals (more than 1 year) and lose calves during the period between calving and weaning. Body depth had a significant influence on incidence of stillbirths and abortions but not mortality of calves from birth to weaning. As body depth increased, total number of calves lost by a cow from calving to weaning decreased linearly. The rate of decrease in number of calves lost by a cow as body depth increased decreased with increase in parity. Thus, the selection of cow with deep bodies could possibly lead to increased fertility in communal Nguni production. There is, however, need for further analysis on whether the association between linear traits and calving interval, abortions, incidence of stillbirths and pre-weaning losses differ with age using many age groups of cows. This could be a starting point to incorporating linear traits and/or visual appraisal for fertility improvement programmes for beef cattle under extensive production.
Conflict of interest statement Authors have no conflict of interest.
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Please cite this article in press as: Zindove, T.J., Chimonyo, M., Are calving interval, abortions, incidence of stillbirths and pre-weaning losses in Nguni cows associated with linear type traits? Anim. Reprod. Sci. (2015), http://dx.doi.org/10.1016/j.anireprosci.2015.07.002