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Factors affecting abortion, stillbirth and kid mortality in the Goat and Yaez (Goat × ibex)
Small Ruminant Research ELSEVIER
Small Ruminant Research, 13 (1994) 33-40
Factors affecting abortion, stillbirth and kid mortality in the Goat and Yaez ( Goat × Ibex) D. Rattner *'a, J. Riviere a, J.E. Bearman b "The Institute of Animal Research, Kibbutz Lahav, D.N. Negev, 85335, Israel UUnit of Epidemiology and Health Services Evaluation, Faculty of Health Science, Ben Gurion University, Beer-Sheva, lsrael (Accepted 29 April 1993)
Abstract Data on abortions, stillbirths and kid mortality from an experimental herd, used for the development of the Yaez, were analyzed. Total number of embryos was 960. Mortality was divided according to kids' age, to early mortality (during first 48 h), mortality before weaning at 70 d (BWA) and after weaning up to 180 d (AWA). There were more abortions among primiparous does ( 11% ) than among older ones ( 5.3% ). More triplets were aborted ( 13.4% vs. 6.2% ) and/or born dead ( 15.5 % vs. 5.3%) than kids in smaller litters. Season affected mortality of kids before, as well as after, weaning. Rates were 7%, 25.3% and 12.8% BWA for winter, spring and summer born kids, respectively. After weaning 8%, 22.6% and 9.5% died out of winter, spring and summer kids, respectively. Day of birth in season was a significant factor of mortality of kids before and after weaning. Of the kids born during the first l0 d of season, 7.7% died BWA and 8.9% AWA; out of kids that were born from 11 to 20 days, 17.5% died BWA and 16.5% AWA, while 27.2% of the kids that were born after 20 d died BWA and 20.7% died AWA. Mortality rate before and after weaning increased corresponding to the percentage of ibex genes in the dam, the sire and the kid. Combination of low birth weight with hybridization of goat and ibex resulted in increased mortality in all three ages. During the first 48 h of their life average mortality was 4.5%; of kids born up to 1.5 kg with 10-30% ibex genes, 17.6% died; and from the group with more than 30% ibex genes, 33.3% died. Key words: Goat; Ibex; Abortion; Kid mortality
1. Introduction In raising goats for meat, as well as for milk, kid losses in early and later stages is a major problem. Devendra and Burns (1970) cite 55% mortality before the age of 3 months in India. They list several factors affecting kid mortality: 1, low birth weight; 2, young age of the doe; 3, seasonal effects - higher mortality rates in cold vs. hot season; more kids die during wet than dry season. Wilson (1984) surveyed mortality *Corresponding author. 0921-4488/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSD1092 1-4488 ( 9 3 ) E0054-V
rates in three countries in semi-arid Africa where he found 22.3-34.6% before the age of 150 d (weaning). For primiparous does he found more than 40% mortality. As additional factors he mentions season and litter size. In a later paper (Wilson et al., 1985), difference between herds was also important and slightly higher mortality in males was mentioned. Garcia and Gall (1981), found mortality rates between 10--60% surveying many countries, but mainly Latin America. Morand-Fehr (1981) presented data from an intensively managed herd of milk goats, collected during 7 yr and include about 2800 cases (embryos). In total,
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D. Rattner et al. / S m a l l Ruminant Research 13 (1994) 33~10
11.5% of the embryos were lost, 2.8% were aborted, 1% born dead, 2.1% died during parturition or shortly after, 4.2% died before weaning (at 45 d) and 2.4% died later. It is obvious that there are regional differences related to breed and husbandry systems. The data presented here were collected from the experimental herd of the Institute of Animal Research in Lahav, Israel. This herd is kept for the development of the Yaez, a cross of the goat with the wild ibex (Capra ibex nubiana), for the improvement of meat quality (Rattner et al., 1985). This cross serves as an example to the effects of crossbreeding between remote breeds. In 1987, the mortality rate was much higher than usually observed in the herd, due to pneumonia and many other causes. It was assumed that the high numbers may help define factors causing kids losses.
2. Materials and methods The basis of the herd was several hundred local goats, from different breeds of Israel and Sinai, which were crossed with ibexes and their progeny. The herd numbered between 550 to 760 does. Management was semi-extensive; does were grazed most of the year: in the fall, winter and spring in hilly natural pasture and during the summer on wheat stubble fields. This was supplemented with feeds in critical periods like mating time (flushing), late gestation and lactation. The progeny was kept in sheds and fed ad lib. Veterinary care was intensive, daily inspection of the herd, at least two regular weekly visits by a veterinarian, and use of recommended medication. Losses were in five categories: Abortions (A); stillbirths (SB); death within 48 h of parturition (48 h); death between 48 h and weaning (70 days) (BWA); death after weaning until 180 d of age (AWA). The following factors were examined: 1. Kidding season - winter, spring and summer (S); 2. Day in season (DAYS); 3. First parity vs. all the later ones (DA); 4. Expected proportion of ibex genes in the dam (DPER); 5. Sire index which included sire ID and expected proportion of ibex genes in the sire (MATE) ; 6. Kid's sex (SEX); 7. Litter size (LT); 8. Kid's birth weight (BWT); 9. Expected proportion of ibex genes in the kid (KPER). To avoid scaling artifacts, mainly in interactions, actual values were linearly transformed to make them
all in the same range of 1 to 10. Some of the factors, such as S, DA, SEX and LT, are discrete variables. Others, like DAYS, DPER, MATE, BWT and KPER are either continuous or contain too many levels and, therefore, were grouped into three levels only. The results of mortality in the fourth category (died between 48 h and weaning) was chosen to define the levels. This was done because it was the category in which the largest number of deaths occurred. This resulted in a high significance of differences between levels of factors in that category. DAYS division was 0-10, 11-20 and 21-51; DPER three levels: 0%, 1-10% and more than 10%; MATE: 0-10%, 11-49%, 50% and more; KPER: 0-10%, 10<30%, 30% and more; BWT: Kids up to 1.5 kg, more than 1.5 kg up to 2 kg and more than 2 kg. Only kids (or embryos) for which all information was available were included in the analysis. Consequently only 960 cases out of 1172 embryos produced that year were analyzed. Main effects were analyzed by Chi-square test. Firstorder interactions were determined directly from the observed mortality rates, using the basic definition of interaction, as described by Li ( 1964, p. 116). As standard error the pooled SE of the four rates was used (Snedecor and Cochran, 1967, p. 101.)
3. Results
Population size and numbers of aborted, dead and survivors, proportions of losses, and P values for each category and main effect are given in Table 1. Differences found with P > 0 . 0 5 for main effects were 'trends'. Only interactions P < 0.01 are discussed. No difference in losses existed between sexes in any of the categories.
3.1. Abortions There were two main effects that were significant, DA and LT. Does that gave birth for the first time aborted more frequently than older does. Does carrying triplets tended to abort more frequently than does with twins or singles. A trend was seen in higher abortion rate in summer kidding. No interactions were found.
D. Rattner et al. /Small Ruminant Research 13 (1994) 33-40
35
Table 1 Mortality in the different categories due to main effects in 1987~ Abortions (%)
Season Winter Spring Summer
6.58 5.81 10.00
P
Stillbirth (%)
48 h (%)
1
4.48 4.16 6.03
5.07 5.23 8.17
0.005
7. I I 5.70
0.9
3.48 6.99 8.00
0.75
Day in season 0-10 1-20 21-51
5.63 5.97 7.20
P
Doe age Young Adult
10,97 5,26
DPER b 0% 1-10% > 10%
5.26 7.47 6.83
Mate 0% 5-49% >/50%
4.29 9.30 6.85
0.5
4.48 7.05 6.40
Sex Male Female
7.47 5.76
0.9
6.58 5.42
Litter size l 2 3
8.41 4.74 13.43
0.05
2.53 7.10 15.52
Total
6.67
0.9
3.03 6.84 7.43 6.03
P
After weaning (%)
0.95
0.75
5.34 4.01 4.66
1
7.65 17.49 27.23
0.001
8.89 16.46 20.73
0,5
6.12 4.03
0.25
24.46 15.83
0.01
19.42 14.40
0.25
0.5
3.61 5.46 6.52
0.9
8.99 21.13 25.58
0.001
7.4 I 19.63 21.88
0.001
0.9
1.88 6.90 4.97
0.25
6.70 14.81 23.53
0.001
7.18 13.04 20.86
0.001
0.5
4.32 4.74
0.9
17.81 17.80
l
15.90 14.97
0.75
0.5
17.45 17.79 20.45
1
15.45 15.57 14.29
0.001
34.67 22.54 12.81
0.001
28.57 12,70 15.17
0,025
0.1
6.42 17.18 29.57
0.001
6.37 16.33 25.31
0.001
0.005
3.25 4.75 10.20
19.79 3.94 1.83
5.33 7.48 6.60
Before weaning (%)
7.03 25.34 12.84
Birth weight ~< 1.5 > 1.5 ~<2 >2 KPEW 0%-10% > 10 ~<30% > 30%
P
0.5
2.68 3.53 7.63 4.52
17.81
0.001
7.98 22.63 9.47
0.001
0.05
15.45
~Total numbers in the categories were: abortions 64 out of 960; stillbirths 54 out of 895; died during 48 h 38 out of 841; died before weaning 143 out of 803; died after weaning 102 out of 660. bDPER = expected proportion of ibex genes in the dam. ~'KPER = expected proportion of ibex genes in the kid,
36
D. Rattner et a l . / Small Ruminant Research 13 (1994) 33~10
3.2. Stillbirths The only significant factor was litter size. Kids of triplets were born dead more often than kids of smaller litters. Some trends were: higher rate later in the season, more cases among primiparous does, increased rate with increased ibex gene percentage in does, increased rate with increased ibex gene percentage in kids. 3.3. Died within 48 h The only significant factor was kid's BWT. Mortality of kids weighing up to 1.5 kg at birth was 19.8%, while for more than 1.5 kg and up to 2 kg 3.9% died; and for over 2 kg only 1.8% died. Interaction between BWT and KPER was significant. Death rates of light (up to 1.5 kg) vs. heavier kids in the three levels of KPER were 0.038 vs. 0.025; 0.176 vs. 0.021 and 0.333 vs. 0.033, respectively. Other trends were higher mortality for kids of primiparous does, increased mortality with
increasing proportion of the does' ibex percentage, increased mortality with increasing proportion of the mate's ibex percentage, higher mortality in larger litters.
3.4. Died before weaning In this category most of the main effects were significant, as were many interactions between main effects. In winter, mortality was lowest at 7%, while in spring it was highest at 25.3%. Summer mortality was 12.8%, about half that of the spring. Kids of primiparous does died more often. There was an increase in death rate with increasing proportions of ibex genes in each parent, and with increased ibex percentage of the kid itself. More kids with lower birth weight died than kids with higher birth weight. The trend of higher mortality of kids from triplets remained.
1987 SEASONBY MATE IBEX PERCENTAGE MORTAUTY
1987 BIRTH DAY IN S E A S O N
MATE
BY
MORTAU'~ RATE
RATE
0.4 [
0.4 ,
I
1
o, ii
c2 ]
~
0.2-
1
0.1 J
o
.
i
I ] io% I 5~*-49X I >=50%
WINTER o.o19 0.049 0.106
~ I
OZ
SPRING 0.123 0.235 0.285
il
SUMMER 0 0.064 0.29
= [
r'! ,
0-1o
'
[~
5%-49%
0.3
~
5%--49%
~
>=50%
1987 PARITY BY KID IBEX PERCENTAGE
MORTAU~ RATE
0.4
i
MORTALITY RATE
0.3
0,2
0.2
0.1
G.1 O
0
o~ E >=50%
0.107 0.163 0.331
MATE IBEX PERCENTAGE I 1 ~ 0%
I---q > : 5 o %
1987 PARITY BY MATE IBEX PERCENTAGE 0.4
21-51
I "1
0.1,4,3 0.12 0.202
MATE IBEX PERCENTAGE or.
11-2o
0.033 0.066 0.138
j 0%
0.04 0.328
I
ADULT
i
0.087
i MATE IBEX PERCENTAGE
!
=
I0%mI0%
oo,
i>10%<=30~
0.206
I>30%
0.026 0.26 0.347
0.073 0.149 0.272 KID IBEX PERCENTAGE
C D Fig. 1. First degree interaction of main effects in mortality before weaning. Probabilities: A, P_< 0.05; B, P _<0.05; C, P < 0.01; D, P < 0.02.
D. Rattner et al. / Small Ruminant Research 13 (1994) 33~10
1987 SEASON BY KIDS' IBEX PERCENTAGE
1987 SEASON BY BIRTH WEIGHT 0,"
37
MORTAUTY RATE
MORTALITY RATE
0.4
O. C.2
C.
...................................................
C C
<=1.5 > 1.5<
1>3o, =
>2
[
WINTER
1
;.;;;
,
~
>1.5<=2
SUMMER
;::;;
!
KIDS' BIRTH WEIGHT
<=1.s
SPRING
KID IBEX PERCENTAGE
~
>2
1987 D A Y OF KIDDING IN S E A S O N
mmo~-10~
1987 DAY OF KIDDING IN SEASON BY MATE
BY D P E R
MORTALITY RATE 0.4 I
C.4
0.3
0.3
. . . . . . . . . . . . . . . . . . . . . . . . . .
r--l>3o,
~>~0,<=30%
MORTALITY RATE .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
0.2
i!iii
!iiii
iiiii
5X-49% i >so~
1i
0.~2
O. 126
O. 139
o.zo3
o.2ez
DAY OF KIDDING IN SEASON
DAY OF KIDDING IN SEASON
DOE IBEX PERCENTAGE
MATE IBEX PERCENTAGE
Fig. 2. First degree interaction of main effects in mortality after weaning. Probabilities: A, P < 0.1; B, P _<0.05; C, P < 0.01 ; D, P < 0.05.
In winter the death rate of kids born late in the season was lower, while in spring the increase was linear from beginning to end of the season. In summer, it was similar, but differences were not significant. In winter and summer, the number of kids born late in the season was low, winter, 26 (10%); spring, 175 (40%); summer, 24 (22%). In winter and summer, mortality was higher among kids of adult does; in spring, higher mortality rate was observed among first parity kids. The majority of primiparous does kidded in spring (winter 19 (10.3%); spring 150 (81.5%); summer 15 (8.2%)). While in spring there was an increase of mortality rate with increase in the does' ibex gene percentage, in winter and summer, the increase occurred only from does with 0% ibex genes to does with moderate ( 1 10%) ibex gene percentage. In does with higher ibex gene contents, the mortality rate declined; but the num-
ber of births in these two groups was very small, 17 and 16 in winter and summer, respectively. In all seasons, there was an increase in mortality with increase in sire ibex gene percentage (Fig. IA). In kids of 0% ibex bucks, mortality increased in the second interval during the season, then decreased (Fig. 1B). In the crossed male progeny, there was an increase in mortality rate from one interval to the following with increase in ibex genes percentage. In kids of pure goat bucks (0% ibex) mortality was lower at first than in later parities (Fig. 1C), while in others mortality was higher at first parity. In kids with low ibex percentage (0-10%), the death rate increased from first to later parities (Fig. 1D) in kids with higher ibex percentage, it decreased. This resulted from the small number of low percentage first parity kids. In does with less than 10% ibex genes, mortality rate
38
D. Rattner et al. /Small Ruminant Research 13 (1994) 33-40
decreased with increasing birth weight. When the does' ibex gene proportion was higher than 10%, mortality rate was high in heavier kids as well. In pure goat bucks, there was no mortality difference between different weight groups. In bucks with moderate ibex gene content, there was high mortality only in small ( < 1.5) kids. In bucks with high ibex percentage, there was a decrease in mortality with increasing weight.
ibex gene proportion, the increase was already prevalent when kidding occurred after 10 days; and in does with higher proportion, the rate of kid losses was high, no matter when they gave birth. Day of birth in season affected only the mortality of kids sired by bucks with more than 50% ibex genes (Fig. 2D). The numbers of 0% bucks progeny were small.
3.5. Died after weaning
4. Discussion
The difference between primiparous does and older ones was not significant, although the trend still existed. Mortality in the spring was much higher than in the two other seasons, the difference between summer and winter was very small (in favour of winter). Increasing mortality with the advance of the season appeared AWA. Ibex proportion of does' genome was a very significant factor; difference was between pure goats and various crosses, but not between different degrees of crossing. Mate and kids' ibex gene proportions were also significant AWA. Kids' BWT was a factor of mortality; although at this age the difference was only between kids that weighed less than 1.6 kg and all the others (Table l). Increased mortality with the advance of season was apparent only during spring. In winter the rates were 5.5%, 9.3% and 4.5%, in spring 6.2%, 11.1% and 13.2%, and in summer 10.5%, 14% and 5.7% for early, mid and late days in season, respectively. In winter there was an increase in kids' mortality rate from 0% ibex to crossbred mates, but no significant difference between degrees of crossing. In spring and summer there was also an increase in mortality from moderate to high proportion of ibex genes in the mate. In kids' BWT groups in winter and summer, there was a very sharp drop in mortality (Fig. 2A) from 2729% of the kids born under 1.6 kg to 6-7% in heavier kids; in spring, mortality was more than 20% in all BWT groups. In winter, there was an increase in mortality from the KPER group of less than 10% ibex genes to all others (Fig. 2B). In spring, mortality increased corresponding to the increase in KPER. In summer, mortality increased only from 30% ibex genes upwards. In pure goats, mortality rate increased only when kidding occurred after 20 days or more from the beginning of the season (Fig. 2C). In does with 10% or less
The plan of matings and other aspects of husbandry had not been carried out with the intention of studying factors of kids survival. It was obvious that in many of our comparisons, the different groups were unbalanced. Three especially important deviations from equal sample sizes were: The number of births per season (winter- 304, spring - 516 and s u m m e r - 140). The large number of embryos sired by bucks with more than 50% ibex genes: 555 vs. 405 in the two other groups combined. The mating of does from different DPER groups with sires of different MATE groups was done according to the Yaez breeding program, and was not random. In several cases, the results deviated from the general trend due to the small group size. It was our conclusion that the minimum reliable group size should not be less than 30 observations. Another point was that 1987 may be called an epidemic year in the sense that loss rates were much higher than usual. This was true for spring losses after weaning, but also in other category-season combinations. Although it gave large samples for statistical analyses, the conclusions may be valid only if we assume that there is no interaction between the epidemic situation and some of the factors examined. Higher rate of abortions in primiparous does may probably arise as a result of lower immunity older does having more chance to experience abortive pathogens and to develop immunity. Kids of primiparous does were at a greater risk in all categories, although the effect was highly significant from 2 to 70 d only. An explanation will be that younger does' colostrum is not as rich in antibodies, quantitatively and qualitatively, as older does'. The amount of milk produced by younger does is usually smaller than the amount produced by more mature ones. Therefore kids born in first
D. Rattner et al. / Small Ruminant Research 13 (1994) 33~I0
kidding does are less well nourished, and less protected against pathogens. Frequent occurrence of abortions in does carrying triplets may be related to the load of such a gestation. Litters of three were also at greater risk of stillbirth, possibly for the same reasons. Lower birth weight was a significant factor of losses in all three periods of kids' life. During the first 48 h 19.8% of the kids born under 1.6 kg died vs. 2.6% of the heavier ones. Between 48 h and 70 d (weaning) 34.7% of the light BWT kids died vs. 16.1% of the heavier; from weaning to age of 6 mo the rates were 28.6% vs. 14.4%. Low BWT with respect to kids' mortality is mentioned by most researchers as causing losses, although the definition differs according to breed. Season affected mortality rate before and after weaning significantly. In winter the proportion of losses was lowest; in spring highest. Losses of kids before weaning in summer was between the two; while after weaning, the difference between summer and winter was small in favour of winter. There was only one important interaction, rates of death after weaning of kids born under 1.6 kg were the same in all three seasons, but the number of these kids was small - between 15 and 17 in each season. Increase of mortality rate in the spring-born kids, especially in relation to winter, was interesting. Higher mortality of kids is found usually in the wet and cold season. Winter in Israel is the season of rain and cold. Goats' main kidding season in this country is in spring. One would expect that natural selection would favour survival in the main kidding season. For climatic conditions, from April to August the temperature differential between day and night is high, on the average more than 12°C, but very often more than 15°C. This may cause stress that weakens the kids' ability to survive. An additional possible explanation to the high rate of mortality in spring is the load on workers and the result that kids do not get the same amount of care in the crowded spring as in other seasons. A correlation of r = 0.67 was found by us between the number of kids born in each year and the rate of losses between birth and weaning (Morand-Fehr, 1981 ). Day of birth in the season was significant in the periods before and after weaning. The shed is usually cleaned and prepared between the kidding seasons, but not during the season. It is reasonable to hypothesize that the pathogen pop-
39
ulation, which is low at the onset of kidding, is built up with the advance of the season so that kids that are born later face a more massive challenge, with which some of them fail to cope. Genetic constitution of the animals was a major risk factor to kid survival. Although this is a special case of an interspecies cross, higher mortality of hybrid kids from a cross of indigenous goats with exotic breeds has been observed (Garcia and Gall, 1981; Devendra and Burns, 1970). Crosses like this are usually used to improve the performance of one or several traits in locally common breeds. Many attempts have failed because of decreased viability of the offspring. The immunological system of the hybrids may not be as efficient as that of the pure goats'. We do not, however, have data on the survival of pure ibexes in general, and in domestic husbandry in particular. In the wild as well as in captivity, ibexes live in small flocks with plenty of space, and normally enjoy generous supplies of food. It is possible that adaptation to a crowded environment as in a commercial herd was not a priority in natural selection. 4.1. Practical implications
In spite of their comparatively high reproduction rate, meat production in goats is slow, while the monetary value of the animals is low. This does not favour high investments in housing, feeding and labour for their improvement. Two factors that had high mortality cannot be controlled: litter size and first kidding. In extensive and even semi-intensive systems one should be aware of the fact that more than two kids per birth is a disadvantage. To minimize losses of triplets, adequate feeding of the does during gestation, particularly during the last third of it, is very important. As for primiparous does, special attention should be paid to the kids, in addition to proper nutrition of the does during gestation. An additional amount of colostrum saved from older does should be very helpful. Avoiding spring kidding completely is not practical at present, as it will result in a lower reproduction rate, a significant proportion of the goats will not kid in other seasons. If our assumption on the temperature effect is correct, the offspring should be housed in a place were temperature difference between day and night will be minimal. During the hot hours of the day the young kids must be kept in the shade. Attention to these two
40
D. Rattner et al. / Small Ruminant Research 13 (1994) 33~10
factors may decrease the temperature difference and the stress causing mortality. As for the late-in-season effect, or the increase in mortality with the advance of season, matings should be performed in short periods of 20 d each. This is approximately the length of the doe's oestrous cycle. Such a period should be started every 2 mo, within the local goats breeding season. This regime will give uniform groups of kids. Goats that fail to conceive in one period will have another chance within a short time later. An alternative approach may be to keep several kidding sheds, each cleaned and prepared before the onset of the season, and the kidding of each ten day period housed in a different shed. Kid's birth weight may be partially controlled by augmenting the does' feeding during the last third of the gestation. Addition of a proper amount of feed over the normal amount fed to the herd should result in an increase of kid's birth weight and lower mortality.
References Devendra, C. and Bums, M., 1970. Goat Production in the Tropics. C.A.B. Famham Royal, Bucks, UK, 184 pp. Garcia, O. and Gall, C., 1981. Goats in the Dry Tropics. In: C. Gall (Ed.), Goat Production, Academic Press, London, UK, pp. 515556. Li, C.C., 1964. Introduction to Experimental Statistics. McGrawHill, New York. Morand-Fehr, P., 1981. Growth. In: C. Gall (Ed.), Goat Production, Academic Press, London, UK, pp. 253-283. Rattner, D., Hillel, J., Moav, R., Levin, I. and Avidan, N., 1985. The Yaez, a cross of the wild Ibex with the domestic goat as a new farm animal. World Rev. Anim. Prod., 21: 59~)4. Snedecor, G.W. and Cochran, W.G., 1967. Statistical Methods. Sixth edn., Iowa State University Press, Ames, IA. Wilson, R.T., 1984. Indigenous Goats: Productivity in traditional livestock systems of semi-arid Africa. Int. Goat Sheep Res., 2: 243-251. Wilson, R.T., Peacock, C.P. and Sayers, A.R., 1985. Pre-weaning mortality and productivity indices for goat and sheep on a Masai group ranch in South-Central Kenya. Anita. Prod., 41:201-206.
Small Ruminant Research, 13 (1994) 33-40
Factors affecting abortion, stillbirth and kid mortality in the Goat and Yaez ( Goat × Ibex) D. Rattner *'a, J. Riviere a, J.E. Bearman b "The Institute of Animal Research, Kibbutz Lahav, D.N. Negev, 85335, Israel UUnit of Epidemiology and Health Services Evaluation, Faculty of Health Science, Ben Gurion University, Beer-Sheva, lsrael (Accepted 29 April 1993)
Abstract Data on abortions, stillbirths and kid mortality from an experimental herd, used for the development of the Yaez, were analyzed. Total number of embryos was 960. Mortality was divided according to kids' age, to early mortality (during first 48 h), mortality before weaning at 70 d (BWA) and after weaning up to 180 d (AWA). There were more abortions among primiparous does ( 11% ) than among older ones ( 5.3% ). More triplets were aborted ( 13.4% vs. 6.2% ) and/or born dead ( 15.5 % vs. 5.3%) than kids in smaller litters. Season affected mortality of kids before, as well as after, weaning. Rates were 7%, 25.3% and 12.8% BWA for winter, spring and summer born kids, respectively. After weaning 8%, 22.6% and 9.5% died out of winter, spring and summer kids, respectively. Day of birth in season was a significant factor of mortality of kids before and after weaning. Of the kids born during the first l0 d of season, 7.7% died BWA and 8.9% AWA; out of kids that were born from 11 to 20 days, 17.5% died BWA and 16.5% AWA, while 27.2% of the kids that were born after 20 d died BWA and 20.7% died AWA. Mortality rate before and after weaning increased corresponding to the percentage of ibex genes in the dam, the sire and the kid. Combination of low birth weight with hybridization of goat and ibex resulted in increased mortality in all three ages. During the first 48 h of their life average mortality was 4.5%; of kids born up to 1.5 kg with 10-30% ibex genes, 17.6% died; and from the group with more than 30% ibex genes, 33.3% died. Key words: Goat; Ibex; Abortion; Kid mortality
1. Introduction In raising goats for meat, as well as for milk, kid losses in early and later stages is a major problem. Devendra and Burns (1970) cite 55% mortality before the age of 3 months in India. They list several factors affecting kid mortality: 1, low birth weight; 2, young age of the doe; 3, seasonal effects - higher mortality rates in cold vs. hot season; more kids die during wet than dry season. Wilson (1984) surveyed mortality *Corresponding author. 0921-4488/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSD1092 1-4488 ( 9 3 ) E0054-V
rates in three countries in semi-arid Africa where he found 22.3-34.6% before the age of 150 d (weaning). For primiparous does he found more than 40% mortality. As additional factors he mentions season and litter size. In a later paper (Wilson et al., 1985), difference between herds was also important and slightly higher mortality in males was mentioned. Garcia and Gall (1981), found mortality rates between 10--60% surveying many countries, but mainly Latin America. Morand-Fehr (1981) presented data from an intensively managed herd of milk goats, collected during 7 yr and include about 2800 cases (embryos). In total,
34
D. Rattner et al. / S m a l l Ruminant Research 13 (1994) 33~10
11.5% of the embryos were lost, 2.8% were aborted, 1% born dead, 2.1% died during parturition or shortly after, 4.2% died before weaning (at 45 d) and 2.4% died later. It is obvious that there are regional differences related to breed and husbandry systems. The data presented here were collected from the experimental herd of the Institute of Animal Research in Lahav, Israel. This herd is kept for the development of the Yaez, a cross of the goat with the wild ibex (Capra ibex nubiana), for the improvement of meat quality (Rattner et al., 1985). This cross serves as an example to the effects of crossbreeding between remote breeds. In 1987, the mortality rate was much higher than usually observed in the herd, due to pneumonia and many other causes. It was assumed that the high numbers may help define factors causing kids losses.
2. Materials and methods The basis of the herd was several hundred local goats, from different breeds of Israel and Sinai, which were crossed with ibexes and their progeny. The herd numbered between 550 to 760 does. Management was semi-extensive; does were grazed most of the year: in the fall, winter and spring in hilly natural pasture and during the summer on wheat stubble fields. This was supplemented with feeds in critical periods like mating time (flushing), late gestation and lactation. The progeny was kept in sheds and fed ad lib. Veterinary care was intensive, daily inspection of the herd, at least two regular weekly visits by a veterinarian, and use of recommended medication. Losses were in five categories: Abortions (A); stillbirths (SB); death within 48 h of parturition (48 h); death between 48 h and weaning (70 days) (BWA); death after weaning until 180 d of age (AWA). The following factors were examined: 1. Kidding season - winter, spring and summer (S); 2. Day in season (DAYS); 3. First parity vs. all the later ones (DA); 4. Expected proportion of ibex genes in the dam (DPER); 5. Sire index which included sire ID and expected proportion of ibex genes in the sire (MATE) ; 6. Kid's sex (SEX); 7. Litter size (LT); 8. Kid's birth weight (BWT); 9. Expected proportion of ibex genes in the kid (KPER). To avoid scaling artifacts, mainly in interactions, actual values were linearly transformed to make them
all in the same range of 1 to 10. Some of the factors, such as S, DA, SEX and LT, are discrete variables. Others, like DAYS, DPER, MATE, BWT and KPER are either continuous or contain too many levels and, therefore, were grouped into three levels only. The results of mortality in the fourth category (died between 48 h and weaning) was chosen to define the levels. This was done because it was the category in which the largest number of deaths occurred. This resulted in a high significance of differences between levels of factors in that category. DAYS division was 0-10, 11-20 and 21-51; DPER three levels: 0%, 1-10% and more than 10%; MATE: 0-10%, 11-49%, 50% and more; KPER: 0-10%, 10<30%, 30% and more; BWT: Kids up to 1.5 kg, more than 1.5 kg up to 2 kg and more than 2 kg. Only kids (or embryos) for which all information was available were included in the analysis. Consequently only 960 cases out of 1172 embryos produced that year were analyzed. Main effects were analyzed by Chi-square test. Firstorder interactions were determined directly from the observed mortality rates, using the basic definition of interaction, as described by Li ( 1964, p. 116). As standard error the pooled SE of the four rates was used (Snedecor and Cochran, 1967, p. 101.)
3. Results
Population size and numbers of aborted, dead and survivors, proportions of losses, and P values for each category and main effect are given in Table 1. Differences found with P > 0 . 0 5 for main effects were 'trends'. Only interactions P < 0.01 are discussed. No difference in losses existed between sexes in any of the categories.
3.1. Abortions There were two main effects that were significant, DA and LT. Does that gave birth for the first time aborted more frequently than older does. Does carrying triplets tended to abort more frequently than does with twins or singles. A trend was seen in higher abortion rate in summer kidding. No interactions were found.
D. Rattner et al. /Small Ruminant Research 13 (1994) 33-40
35
Table 1 Mortality in the different categories due to main effects in 1987~ Abortions (%)
Season Winter Spring Summer
6.58 5.81 10.00
P
Stillbirth (%)
48 h (%)
1
4.48 4.16 6.03
5.07 5.23 8.17
0.005
7. I I 5.70
0.9
3.48 6.99 8.00
0.75
Day in season 0-10 1-20 21-51
5.63 5.97 7.20
P
Doe age Young Adult
10,97 5,26
DPER b 0% 1-10% > 10%
5.26 7.47 6.83
Mate 0% 5-49% >/50%
4.29 9.30 6.85
0.5
4.48 7.05 6.40
Sex Male Female
7.47 5.76
0.9
6.58 5.42
Litter size l 2 3
8.41 4.74 13.43
0.05
2.53 7.10 15.52
Total
6.67
0.9
3.03 6.84 7.43 6.03
P
After weaning (%)
0.95
0.75
5.34 4.01 4.66
1
7.65 17.49 27.23
0.001
8.89 16.46 20.73
0,5
6.12 4.03
0.25
24.46 15.83
0.01
19.42 14.40
0.25
0.5
3.61 5.46 6.52
0.9
8.99 21.13 25.58
0.001
7.4 I 19.63 21.88
0.001
0.9
1.88 6.90 4.97
0.25
6.70 14.81 23.53
0.001
7.18 13.04 20.86
0.001
0.5
4.32 4.74
0.9
17.81 17.80
l
15.90 14.97
0.75
0.5
17.45 17.79 20.45
1
15.45 15.57 14.29
0.001
34.67 22.54 12.81
0.001
28.57 12,70 15.17
0,025
0.1
6.42 17.18 29.57
0.001
6.37 16.33 25.31
0.001
0.005
3.25 4.75 10.20
19.79 3.94 1.83
5.33 7.48 6.60
Before weaning (%)
7.03 25.34 12.84
Birth weight ~< 1.5 > 1.5 ~<2 >2 KPEW 0%-10% > 10 ~<30% > 30%
P
0.5
2.68 3.53 7.63 4.52
17.81
0.001
7.98 22.63 9.47
0.001
0.05
15.45
~Total numbers in the categories were: abortions 64 out of 960; stillbirths 54 out of 895; died during 48 h 38 out of 841; died before weaning 143 out of 803; died after weaning 102 out of 660. bDPER = expected proportion of ibex genes in the dam. ~'KPER = expected proportion of ibex genes in the kid,
36
D. Rattner et a l . / Small Ruminant Research 13 (1994) 33~10
3.2. Stillbirths The only significant factor was litter size. Kids of triplets were born dead more often than kids of smaller litters. Some trends were: higher rate later in the season, more cases among primiparous does, increased rate with increased ibex gene percentage in does, increased rate with increased ibex gene percentage in kids. 3.3. Died within 48 h The only significant factor was kid's BWT. Mortality of kids weighing up to 1.5 kg at birth was 19.8%, while for more than 1.5 kg and up to 2 kg 3.9% died; and for over 2 kg only 1.8% died. Interaction between BWT and KPER was significant. Death rates of light (up to 1.5 kg) vs. heavier kids in the three levels of KPER were 0.038 vs. 0.025; 0.176 vs. 0.021 and 0.333 vs. 0.033, respectively. Other trends were higher mortality for kids of primiparous does, increased mortality with
increasing proportion of the does' ibex percentage, increased mortality with increasing proportion of the mate's ibex percentage, higher mortality in larger litters.
3.4. Died before weaning In this category most of the main effects were significant, as were many interactions between main effects. In winter, mortality was lowest at 7%, while in spring it was highest at 25.3%. Summer mortality was 12.8%, about half that of the spring. Kids of primiparous does died more often. There was an increase in death rate with increasing proportions of ibex genes in each parent, and with increased ibex percentage of the kid itself. More kids with lower birth weight died than kids with higher birth weight. The trend of higher mortality of kids from triplets remained.
1987 SEASONBY MATE IBEX PERCENTAGE MORTAUTY
1987 BIRTH DAY IN S E A S O N
MATE
BY
MORTAU'~ RATE
RATE
0.4 [
0.4 ,
I
1
o, ii
c2 ]
~
0.2-
1
0.1 J
o
.
i
I ] io% I 5~*-49X I >=50%
WINTER o.o19 0.049 0.106
~ I
OZ
SPRING 0.123 0.235 0.285
il
SUMMER 0 0.064 0.29
= [
r'! ,
0-1o
'
[~
5%-49%
0.3
~
5%--49%
~
>=50%
1987 PARITY BY KID IBEX PERCENTAGE
MORTAU~ RATE
0.4
i
MORTALITY RATE
0.3
0,2
0.2
0.1
G.1 O
0
o~ E >=50%
0.107 0.163 0.331
MATE IBEX PERCENTAGE I 1 ~ 0%
I---q > : 5 o %
1987 PARITY BY MATE IBEX PERCENTAGE 0.4
21-51
I "1
0.1,4,3 0.12 0.202
MATE IBEX PERCENTAGE or.
11-2o
0.033 0.066 0.138
j 0%
0.04 0.328
I
ADULT
i
0.087
i MATE IBEX PERCENTAGE
!
=
I0%mI0%
oo,
i>10%<=30~
0.206
I>30%
0.026 0.26 0.347
0.073 0.149 0.272 KID IBEX PERCENTAGE
C D Fig. 1. First degree interaction of main effects in mortality before weaning. Probabilities: A, P_< 0.05; B, P _<0.05; C, P < 0.01; D, P < 0.02.
D. Rattner et al. / Small Ruminant Research 13 (1994) 33~10
1987 SEASON BY KIDS' IBEX PERCENTAGE
1987 SEASON BY BIRTH WEIGHT 0,"
37
MORTAUTY RATE
MORTALITY RATE
0.4
O. C.2
C.
...................................................
C C
<=1.5 > 1.5<
1>3o, =
>2
[
WINTER
1
;.;;;
,
~
>1.5<=2
SUMMER
;::;;
!
KIDS' BIRTH WEIGHT
<=1.s
SPRING
KID IBEX PERCENTAGE
~
>2
1987 D A Y OF KIDDING IN S E A S O N
mmo~-10~
1987 DAY OF KIDDING IN SEASON BY MATE
BY D P E R
MORTALITY RATE 0.4 I
C.4
0.3
0.3
. . . . . . . . . . . . . . . . . . . . . . . . . .
r--l>3o,
~>~0,<=30%
MORTALITY RATE .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
0.2
i!iii
!iiii
iiiii
5X-49% i >so~
1i
0.~2
O. 126
O. 139
o.zo3
o.2ez
DAY OF KIDDING IN SEASON
DAY OF KIDDING IN SEASON
DOE IBEX PERCENTAGE
MATE IBEX PERCENTAGE
Fig. 2. First degree interaction of main effects in mortality after weaning. Probabilities: A, P < 0.1; B, P _<0.05; C, P < 0.01 ; D, P < 0.05.
In winter the death rate of kids born late in the season was lower, while in spring the increase was linear from beginning to end of the season. In summer, it was similar, but differences were not significant. In winter and summer, the number of kids born late in the season was low, winter, 26 (10%); spring, 175 (40%); summer, 24 (22%). In winter and summer, mortality was higher among kids of adult does; in spring, higher mortality rate was observed among first parity kids. The majority of primiparous does kidded in spring (winter 19 (10.3%); spring 150 (81.5%); summer 15 (8.2%)). While in spring there was an increase of mortality rate with increase in the does' ibex gene percentage, in winter and summer, the increase occurred only from does with 0% ibex genes to does with moderate ( 1 10%) ibex gene percentage. In does with higher ibex gene contents, the mortality rate declined; but the num-
ber of births in these two groups was very small, 17 and 16 in winter and summer, respectively. In all seasons, there was an increase in mortality with increase in sire ibex gene percentage (Fig. IA). In kids of 0% ibex bucks, mortality increased in the second interval during the season, then decreased (Fig. 1B). In the crossed male progeny, there was an increase in mortality rate from one interval to the following with increase in ibex genes percentage. In kids of pure goat bucks (0% ibex) mortality was lower at first than in later parities (Fig. 1C), while in others mortality was higher at first parity. In kids with low ibex percentage (0-10%), the death rate increased from first to later parities (Fig. 1D) in kids with higher ibex percentage, it decreased. This resulted from the small number of low percentage first parity kids. In does with less than 10% ibex genes, mortality rate
38
D. Rattner et al. /Small Ruminant Research 13 (1994) 33-40
decreased with increasing birth weight. When the does' ibex gene proportion was higher than 10%, mortality rate was high in heavier kids as well. In pure goat bucks, there was no mortality difference between different weight groups. In bucks with moderate ibex gene content, there was high mortality only in small ( < 1.5) kids. In bucks with high ibex percentage, there was a decrease in mortality with increasing weight.
ibex gene proportion, the increase was already prevalent when kidding occurred after 10 days; and in does with higher proportion, the rate of kid losses was high, no matter when they gave birth. Day of birth in season affected only the mortality of kids sired by bucks with more than 50% ibex genes (Fig. 2D). The numbers of 0% bucks progeny were small.
3.5. Died after weaning
4. Discussion
The difference between primiparous does and older ones was not significant, although the trend still existed. Mortality in the spring was much higher than in the two other seasons, the difference between summer and winter was very small (in favour of winter). Increasing mortality with the advance of the season appeared AWA. Ibex proportion of does' genome was a very significant factor; difference was between pure goats and various crosses, but not between different degrees of crossing. Mate and kids' ibex gene proportions were also significant AWA. Kids' BWT was a factor of mortality; although at this age the difference was only between kids that weighed less than 1.6 kg and all the others (Table l). Increased mortality with the advance of season was apparent only during spring. In winter the rates were 5.5%, 9.3% and 4.5%, in spring 6.2%, 11.1% and 13.2%, and in summer 10.5%, 14% and 5.7% for early, mid and late days in season, respectively. In winter there was an increase in kids' mortality rate from 0% ibex to crossbred mates, but no significant difference between degrees of crossing. In spring and summer there was also an increase in mortality from moderate to high proportion of ibex genes in the mate. In kids' BWT groups in winter and summer, there was a very sharp drop in mortality (Fig. 2A) from 2729% of the kids born under 1.6 kg to 6-7% in heavier kids; in spring, mortality was more than 20% in all BWT groups. In winter, there was an increase in mortality from the KPER group of less than 10% ibex genes to all others (Fig. 2B). In spring, mortality increased corresponding to the increase in KPER. In summer, mortality increased only from 30% ibex genes upwards. In pure goats, mortality rate increased only when kidding occurred after 20 days or more from the beginning of the season (Fig. 2C). In does with 10% or less
The plan of matings and other aspects of husbandry had not been carried out with the intention of studying factors of kids survival. It was obvious that in many of our comparisons, the different groups were unbalanced. Three especially important deviations from equal sample sizes were: The number of births per season (winter- 304, spring - 516 and s u m m e r - 140). The large number of embryos sired by bucks with more than 50% ibex genes: 555 vs. 405 in the two other groups combined. The mating of does from different DPER groups with sires of different MATE groups was done according to the Yaez breeding program, and was not random. In several cases, the results deviated from the general trend due to the small group size. It was our conclusion that the minimum reliable group size should not be less than 30 observations. Another point was that 1987 may be called an epidemic year in the sense that loss rates were much higher than usual. This was true for spring losses after weaning, but also in other category-season combinations. Although it gave large samples for statistical analyses, the conclusions may be valid only if we assume that there is no interaction between the epidemic situation and some of the factors examined. Higher rate of abortions in primiparous does may probably arise as a result of lower immunity older does having more chance to experience abortive pathogens and to develop immunity. Kids of primiparous does were at a greater risk in all categories, although the effect was highly significant from 2 to 70 d only. An explanation will be that younger does' colostrum is not as rich in antibodies, quantitatively and qualitatively, as older does'. The amount of milk produced by younger does is usually smaller than the amount produced by more mature ones. Therefore kids born in first
D. Rattner et al. / Small Ruminant Research 13 (1994) 33~I0
kidding does are less well nourished, and less protected against pathogens. Frequent occurrence of abortions in does carrying triplets may be related to the load of such a gestation. Litters of three were also at greater risk of stillbirth, possibly for the same reasons. Lower birth weight was a significant factor of losses in all three periods of kids' life. During the first 48 h 19.8% of the kids born under 1.6 kg died vs. 2.6% of the heavier ones. Between 48 h and 70 d (weaning) 34.7% of the light BWT kids died vs. 16.1% of the heavier; from weaning to age of 6 mo the rates were 28.6% vs. 14.4%. Low BWT with respect to kids' mortality is mentioned by most researchers as causing losses, although the definition differs according to breed. Season affected mortality rate before and after weaning significantly. In winter the proportion of losses was lowest; in spring highest. Losses of kids before weaning in summer was between the two; while after weaning, the difference between summer and winter was small in favour of winter. There was only one important interaction, rates of death after weaning of kids born under 1.6 kg were the same in all three seasons, but the number of these kids was small - between 15 and 17 in each season. Increase of mortality rate in the spring-born kids, especially in relation to winter, was interesting. Higher mortality of kids is found usually in the wet and cold season. Winter in Israel is the season of rain and cold. Goats' main kidding season in this country is in spring. One would expect that natural selection would favour survival in the main kidding season. For climatic conditions, from April to August the temperature differential between day and night is high, on the average more than 12°C, but very often more than 15°C. This may cause stress that weakens the kids' ability to survive. An additional possible explanation to the high rate of mortality in spring is the load on workers and the result that kids do not get the same amount of care in the crowded spring as in other seasons. A correlation of r = 0.67 was found by us between the number of kids born in each year and the rate of losses between birth and weaning (Morand-Fehr, 1981 ). Day of birth in the season was significant in the periods before and after weaning. The shed is usually cleaned and prepared between the kidding seasons, but not during the season. It is reasonable to hypothesize that the pathogen pop-
39
ulation, which is low at the onset of kidding, is built up with the advance of the season so that kids that are born later face a more massive challenge, with which some of them fail to cope. Genetic constitution of the animals was a major risk factor to kid survival. Although this is a special case of an interspecies cross, higher mortality of hybrid kids from a cross of indigenous goats with exotic breeds has been observed (Garcia and Gall, 1981; Devendra and Burns, 1970). Crosses like this are usually used to improve the performance of one or several traits in locally common breeds. Many attempts have failed because of decreased viability of the offspring. The immunological system of the hybrids may not be as efficient as that of the pure goats'. We do not, however, have data on the survival of pure ibexes in general, and in domestic husbandry in particular. In the wild as well as in captivity, ibexes live in small flocks with plenty of space, and normally enjoy generous supplies of food. It is possible that adaptation to a crowded environment as in a commercial herd was not a priority in natural selection. 4.1. Practical implications
In spite of their comparatively high reproduction rate, meat production in goats is slow, while the monetary value of the animals is low. This does not favour high investments in housing, feeding and labour for their improvement. Two factors that had high mortality cannot be controlled: litter size and first kidding. In extensive and even semi-intensive systems one should be aware of the fact that more than two kids per birth is a disadvantage. To minimize losses of triplets, adequate feeding of the does during gestation, particularly during the last third of it, is very important. As for primiparous does, special attention should be paid to the kids, in addition to proper nutrition of the does during gestation. An additional amount of colostrum saved from older does should be very helpful. Avoiding spring kidding completely is not practical at present, as it will result in a lower reproduction rate, a significant proportion of the goats will not kid in other seasons. If our assumption on the temperature effect is correct, the offspring should be housed in a place were temperature difference between day and night will be minimal. During the hot hours of the day the young kids must be kept in the shade. Attention to these two
40
D. Rattner et al. / Small Ruminant Research 13 (1994) 33~10
factors may decrease the temperature difference and the stress causing mortality. As for the late-in-season effect, or the increase in mortality with the advance of season, matings should be performed in short periods of 20 d each. This is approximately the length of the doe's oestrous cycle. Such a period should be started every 2 mo, within the local goats breeding season. This regime will give uniform groups of kids. Goats that fail to conceive in one period will have another chance within a short time later. An alternative approach may be to keep several kidding sheds, each cleaned and prepared before the onset of the season, and the kidding of each ten day period housed in a different shed. Kid's birth weight may be partially controlled by augmenting the does' feeding during the last third of the gestation. Addition of a proper amount of feed over the normal amount fed to the herd should result in an increase of kid's birth weight and lower mortality.
References Devendra, C. and Bums, M., 1970. Goat Production in the Tropics. C.A.B. Famham Royal, Bucks, UK, 184 pp. Garcia, O. and Gall, C., 1981. Goats in the Dry Tropics. In: C. Gall (Ed.), Goat Production, Academic Press, London, UK, pp. 515556. Li, C.C., 1964. Introduction to Experimental Statistics. McGrawHill, New York. Morand-Fehr, P., 1981. Growth. In: C. Gall (Ed.), Goat Production, Academic Press, London, UK, pp. 253-283. Rattner, D., Hillel, J., Moav, R., Levin, I. and Avidan, N., 1985. The Yaez, a cross of the wild Ibex with the domestic goat as a new farm animal. World Rev. Anim. Prod., 21: 59~)4. Snedecor, G.W. and Cochran, W.G., 1967. Statistical Methods. Sixth edn., Iowa State University Press, Ames, IA. Wilson, R.T., 1984. Indigenous Goats: Productivity in traditional livestock systems of semi-arid Africa. Int. Goat Sheep Res., 2: 243-251. Wilson, R.T., Peacock, C.P. and Sayers, A.R., 1985. Pre-weaning mortality and productivity indices for goat and sheep on a Masai group ranch in South-Central Kenya. Anita. Prod., 41:201-206.