30.07.2015

Stages of pregnancy goats

Effect of Dietary Inclusion of Whole Sunflower Seeds on Feeding Lactating Zaraibi Goats: II.
The general trend of change in the mean total solids of goat’s milk during lactation period is in full agreement with those reported by Pal et al. Effect of feeding experimental diets on separation condition of fatty acids (%) of milk is shown in Table 6 where the dietary treatment affected fatty acids composition in milk fat of goats. Furthermore, the peculiarities of goat milk lipolytic system (Chilliard, 1982) and medium-chain fatty acids (Ha and Lindsay, 1993) could greatly change the content in free fatty acids, playing a major role in the occurrence of the characteristic goat flavor. Means of somatic cells count (SSC) during different lactation stages (suckling and milking periods) in the milk of different groups are shown in Table 7.
Hinckley (1991) observed the lowest SCC in milk of goats in April and the highest values in September-October. The histological examination of specimens of the mammary gland of Zaraibi goats showed normal architecture of the mammary gland in all experimental groups; however, some differences were observed as affected by dietary treatment or lactation period in terms of number and size of milk alveoli, number and volume of secretory cells, size as well as area of the mammary stroma (connective tissues). Plate (1): Sections in pre-suckling mammary gland of goats in different experimental groups. The results of an experimental study conducted in northern Kenya on the effects of controlled seasonal breeding on biological performance traits of pastoral goat herds has revealed that such a management practice could effectively reduce the impact of fluctuations in nutrient supply on youngstock survival, mainly through concomitant improvements in birth weights and milk production of dams (Chapters 3 and 5).
The principles outlined in Chapter 6 were utilized to formulate a population dynamics model for pastoral goat herds.
The life history of a breeding female begins with its birth into the juvenile stage (0 to 5 months of age), then it either dies or becomes a weaned female young five months later.
The parity number of does is increased by one whenever a pregnant doe survives until parturition. Metabolizable energy (ME) requirements were assessed according to the factorial method, in which requirements for maintenance, growth, pregnancy, and lactation are estimated separately, and then summed to give the total net requirement (ARC, 1980). Recall that in modelling herd growth, a postbreeding census was assumed, and therefore projected stage abundances refer to those observed at time t in each time interval [t, t+1].
With repect to energy requirements for pregnancy, the approach suggested by NRC (1981) was adopted, which is to increase daily ME requirements per animal by a fixed value of 5.94 MJ during the last two months of pregnancy.
For each life cycle stage, body weight estimates for animals present at the beginning of each time step were available from corresponding stage-specific growth curves (Chapter 4).
Data on empty body and carcass weights for SEA goats were available from an experiment conducted simultaneously to the present study at the Ngare Ndare research station (Hofman an Schwartz, 1987). Whenever average empty body weight at entry into a stage class exceeded the assumed weight at maturity, degree of maturity was set to 1 in calculating gross energy yields. Similarly to the assessment of energy requirements, milk yield and milk offtake per animal present at the start of a time interval [t, t+1] in lactation stage i was adjusted for mortality.
As mentioned above, the parameterisation of the individual herd productivity assessment models was based on results of statistical analyses of experimental data obtained on stage-specific conception, fecundity and survival rates, as well as on liveweight development and milk yields in each of the six different mating season groups. T=time required for a population at stable stage distribution to grow by the net reproductive rate).
0 and λ values obtained through matrix analyses), optimising herd structure and culling policy with respect to energetic efficiency resulted in stationary state stage abundances which maximized net reproductive rates, and therefore offtake per time unit. In order to enhance goat herd productivity in the current production system, management interventions should therefore not primarily be directed towards increasing reproductive output of breeding females. Given that probabilities of surviving and moving into pregnant stages are derived parameters, it is worthwhile investigating the impact of the underlying vital rates on population growth. The results of the herd productivity assessment lead to the conclusion that under the prevailing environmental conditions, confining breeding in pastoral goat herds to the period from June to July (mating season 4) confers a distinctive advantage in terms of all relevant biological efficiency parameters considered.
If maximum energetic efficiency is to be achieved, breeding of goats in the period from December to May should be avoided, irrespective of the amount of milk extracted for human consumption.
During suckling period, at the day of hand-milking, the morning milk from goats of each breed group cooled at 5°C, added to the evening milk, well mixed and representative samples were taken. In Red Sokoto goats, Ehoche and Buvanendran (1983) reported that milk protein content was high in the first week of lactation, declined rapidly to minimum values between the fourth and sixth week, and then increased gradually up to the end of lactation with lower variations from week to week. The response of milk fatty acid composition is nearly similar, in particular for major fatty acids, including conjugated linoleic acid (CLA) in milk of goats in all groups.
However, in another study with goat milk bulk tank samples, SCC did not appear to be affected by seasonal variation (Tirard-Collet et al., 1991).
The procedure is based on a stage-based description of population dynamics and uses non-linear programming to derive the steady state herd structure and culling policy that maximizes overall energetic efficiency of pastoral goatkeeping. The subscripts np(k, l) for non-pregnant stages identify the kth non-pregnant stage for an animal of parity l. The decision to ignore breeding female stage classes beyond the fifth parity was supported by the fact that only 5 out of the 287 fertilisations in the experiment occurred the fifth or higher parity stage. Values of daily ME requirements for maintenance, growth, pregnancy, and lactation were based on those recommended for goats by NRC (1981). Energy released from mobilization of body reserves was also taken into account in calculating total ME requirements for each life history stage. The quantity of milk extracted for human consumption over one projection time step was assumed to correspond to a fixed proportion of expected total milk produced by animals in lactation stages (see the section on model parameterisation and description of scenarios performed further below). The main problem resided in estimating the gross energy content per kg of empty body and carcass weight in different life cycle stages. Relationships between degree of maturity and protein and fat contents in empty bodies of goats (data from Viljoen et al., 1988).
Because very few animals lactated more than four times during the experiment, observations of such animals were pooled with those of parity stage four animals. No information on milk offtake rates per lactation in pastoral goat herds in Kenya was available, and use was made of an expert opinion.
Optimal steady state stage distributions and culling policies (percentage stage abundances and offtake rates) in each mating season group for the baseline scenario, obtained from runs of "average" models. Elasticities of herd growth rate to probabilities of surviving and moving into pregnant stages for the six mating season groups and the aseasonal reference herd (BF = breeding female).


Upon shifting stable stage abundances towards higher parity does, the increase in juvenile mortality also led to a general increase in generation time, which, again, was most pronounced in group 6 (48.1 vs. Increasing productivity of goats will contribute to improve the standard of living of the rural people. The obtained results are in agreement with those observed in milk of Zaraibi goats fed rations contained 5 or 10% SFS (El-Sanafawy, 2008) or fed different types of oils (Hassan et al., 2012). In Damascus, local Barki goats and their crosses, Eissa (1996) found that milk protein content decreased from the first week until the fifth to sixth week, then increased till week 16. Milk of goats fed 20% SFS ration was characterized by absence of palmitoleic acid and presence of linolenic acid.
Intramammary infection in one udder half of goats increased SCC in the corresponding uninfected half (Dulin et al., 1983), which could be an important factor in milk quality testing. Also, Farghaly (2002) showed that stage of lactation significantly affected milk SSC, since both the original and logarithm milk somatic cells were the highest shortly after calving, dropped to a minimum between 40 and 80 days postpartum and then steadily increased until the end of lactation. Seasonal variation may reflect the number of fresh to mid and late lactation does because goats breed seasonally. Continuous breeding throughout the year, which is made possible due to the non-seasonal reproductive behaviour of local goat breeds, is typical for pastoral goat flocks in northern Kenya. As a synthesis of the previous results, the present chapter is concerned with the assessment and comparison of overall biological herd productivity achieved in goat herds subjected to controlled breeding at different time points in a year.
As discussed in Caswell (1989, 1996b), a reducible transition matrix contains at least one stage that cannot contribute, by any development path, to some other stages. The population is divided into two immature stages (birth to 5, and 5 to 10 months of age), one replacement stage, and a total of 38 breeding female stages. Similar reproductive life-spans of SEA goats have been reported by Peacock (1984) and Wilson (1992). Information on this subject is very scarce for tropical goat breeds in general, and are virtually nonexistent for goats of the SEA type. Pastoral goat herds are generally reared as dual purpose meat and milk herds, and milk offtake rates for human consumption affect both survival and growth rates of kids. This was motivated by the fact that the latter factors have previously been argued to be major determinants of goat herd productivity under semi-arid conditions in Africa (Peacock, 1983; Wilson, 1989).
Note that energetic efficiencies for the newborn stage could not be calculated by considering the male herd only since, at birth, cumulative metabolizable energy requirements were assumed to be equal to zero.
These findings are contrary to the results of a sensitivity analysis reported by Peacock (1984), which was aimed at identifying major factors affecting levels of biological productivity in Maasai goat herds. Nevertheless, the herd of SEA goats studied in this experiment seemed to demonstrate relatively low forage energy conversion efficiencies when compared to commercial cattle ranching systems.
In all three groups, significant parts of the lactation stage coincided with the long dry season, during which feed availability was insufficient to cover the nutrient requirements of dams and their progeny.
These results were obtained by assuming that all vital and production parameters corresponded to the mean taken over all mating season groups, and that the average kidding interval in an aseasonally managed goat herd is approximately equal to 10 months. During the last month of pregnancy, all does were divided into three groups (10 does each). Also, results available on goats (Chilliard et al., 2003) showed that milk protein content had no marked changes in goats in responses to dietary fat supplementation.
However, no clear differences in total solids were found between Damascus and Barki goats and their crosses (Eissa, 1996).
Also, feeding goats on 20% SFS ration increased total content of unsaturated fatty acids as well as long chain fatty acids in milk fat. In addition, the changes in SSC in milk of goats may be associated with seasonal variation. The first hypothesis for testing is that there is an optimal period in a year to which breeding can be restricted to improve overall biological productivity of goat flocks. For instance, this occurs with the non-reproducing or surplus male and female parts of the population which form sequences of stages with only one-way communication, i.e. Breeding does which were mated for the first time in their parity class and failed to conceive move through two non-pregnant stages (0 to 5 months and 5 to 12 months) and are rebred the following year. The construction of the life-cycle graph of an aseasonally managed pastoral goat herd was based on the reasoning discussed in Chapter 6. The main reason for this was that selecting a shorter time period would have resulted in a projection time step less than five months, and thus in a more complicated model structure of the model due to the corresponding increase in the number of stages. Information on weight development, weight gain, and lactation yield in all life cycle stages were obtained from growth and lactation curves that were fitted to experimental data (Chapters 4 and 5). Given that longitudinal stage-specific survival data were available, it was possible to estimate survival curves for each life history stage. Schwartz (personal communication) suggested that roughly one third of total lactational milk yield could be considered as an upper limit for milk offtake rates in pastoral goat herds.
Given that the difference in doe survival over lactation and pregnancy stages between both groups was small, leading to similar stable stage abundances in breeding female stages, the lower probability of conception implied that, in mating season 2, a larger proportion of replacement and breeding females would be expected to spend one or more production cycles in an unreproductive stage, thus increasing the average age at all kiddings.
Results of the sensitivity analysis of conception rates are presented here for the baseline scenarios of mating season groups 1 and 4 only, being representative of goat herds with low and high potential growth rates and productive efficiencies. Therefore, the present results may indicate that inclusion of SFS in diets of goats had no effects on milk protein.
Lipid composition is one of the most important components of the technological and nutritional quality of goat milk.
It is of interest to note that values of SSC presented in this study for all groups are higher than that reported in milk of goats. Secondly, a simulated, aseasonally reproducing herd is used as a reference in testing whether controlled breeding in goat herds is superior to uncontrolled breeding under semi-arid rangeland conditions in northern Kenya. It takes one year to complete a full reproductive cycle, which is split up into pregnancy and lactation stages for fertile does, and two consecutive non-pregnant stages for temporarily infertile animals. Then, an appropriate assessment of stage-specific ME requirements for each body function over the interval [t, t+1] would have consisted in summing together the daily requirements for each body function for all days a within [t, t+1], weighted by the probability of surviving until the end of day a.


The few examples on tropical breeds that could be found were those of Gosh and Moitra (1992) on Black Bengal goats, Aganda et al. This corresponds to the lower limit of the range of mature live weights (60 to 75 kg) reported by Devendra and Burns (1983) for female Boer goats. Thus, in the increased milk offtake scenario an offtake rate for human consumption of 33 percent (including the experimental offtake) of all milk produced by does in the different parity stage classes was assumed. Similarly, an offtake policy which harvests an equal proportion of individuals from each stage class would result in offtake rate levels of only 16 (mating season 6) to 56 percent (mating season 3) of those determined by non-linear programming.
However, it should be emphasized that decisions relating to the management of surplus male stages are not independent of the performance, in terms of energetic efficiency, achieved by the female part of a herd.
The impact of changes in the probabilities of surviving and moving into pregnancy stages are somewhat more difficult to interpret, since these entries depend on both the probability of conception and that of surviving over the corresponding stage. For the presently chosen life-cycle structure of goat herds, estimation accuracy of conception rates appear to be more important in determining asymptotic herd growth than productive efficiency.
Generally, there was a tendency to replace breeding females, at least partly, in later parity stages than in the baseline scenario.
Thus, there appears to be some justification for the management practice of Maasai pastoralists in southern Kenya to try to limit breeding activity in their goat flocks to the beginning of the dry season in June, so that births occur during the short dry season (de Leeuw et al., 1991).
The latter example also illustrates that there is little point in trying to enhance reproductive performance in terms of, for instance, the number of kids born per doe exposed, as long as a reasonably high rate of survival of newborns beyond the juvenile stage cannot be guaranteed.In a similar vein, the sensitivity analysis to be presented below shows that kid survival is the single most important vital parameter determining the productivity of goat herds under the prevailing environmental conditions. During the day of milking, kids were removed from their dams and allowed to suckle other goats. Therefore, the surplus stages of both sexes were omitted from the productivity assessment model for carrying out matrix analyses. Nulliparous females are allowed to remain reproductively inactive for a maximum of 36 months, and are culled (or die) if no pregnancy is detected at the end of the third consecutive infertile cycle. In goats, the shortest period from kidding to conception corresponds to the time until occurrence of the first oestrus postpartum, which implies a minimum kidding interval of about 175 days (Devendra and Burns, 1983). However, to reduce the amount of calculation involved, it was decided to divide the five months (or roughly 152 days) projection time interval into intervals of length l=14 days (breeding female stages) and l=56 days (youngstock, replacement, and surplus animal stages).
Based on a similar reasoning, the expected amount of energy available to kids from milk consumed until weaning was accounted for in calculating total metabolizable feed energy requirements per kid present at the beginning of the youngstock stage (0 to 5 months). Estimated probability of conception was also low in this group (86.1 percent), and its impact on generation time was compounded by the fact that higher stable stage abundances of older does were predicted than in the first two mating seasons, because of lower mortality rates over lactation and pregnancy stages for higher parity does. At the late stage of pregnancy (last month of pregnancy, all experimental does (n=30) were divided into three experimental groups according to their age, weight and milk production.
The self-loops attached to the lactation and some of the non-pregnant stages indicate that the duration of these stages exceeds the 5 months projection interval. Wilson (1992) reported mean kidding intervals for goats of the SEA type of 306 days (Maasai), 297 days (Mubende), 233 days (Mashona) and 14 months (Boran). The expected milk produced by lactating does until weaning was estimated from stage-specific lactation curves and survival rates of does until weaning.
The impact of this type of matrix entry declines over successive parturitions due to the reduction in residual reproductive value with advancing parity stage. To cover the various nutrients in goats, energy and protein, the feed concentration should be increased, as these dairy animals have a smaller rumen capacity.
Goats in the 1st  group (G1) served as a control group and were fed the basal ration (control). It is important to take such variations in production goals into account because, traditionally, goats play a crucial role in buffering insecurities and imbalances in food supply to pastoral households and are reared for dual-purpose meat and milk production, while the transition towards a more sedentary life-style increases the pressure on pastoral producers to specialise and commercialise their mode of production. Principally, it is straightforward to extend the time period potentially spent by an animal as reproductively inactive by simply adding further non-pregnant stages to the life cycle graph.
The number of non-pregnant stages by parity class is the same as for the seasonal breeding life cycle, although the maximum duration of reproductive inactivity is reduced to 30 (parity 0) and 20 months (parity ≥ 1). The last study analysed body composition of does over a relatively wide range of ages and live masses for does, and the results reported therein are used here as a basis to estimate gross energy contents per kg of empty body and carcass weight in different life cycle stages.
On the one hand, the large discrepancy between these estimates may be due to the fact that Turkana pastoralists achieve much higher milk offtake rates from their sheep and goat herds than the one third of total lactational milk yield assumed in the increased milk offtake scenario. Oilseeds (sunflower) contribute to increase energy intake of goats and defatted oilseeds in the diet increase the protein intake (Antunac et al., 2001). The reviewed studies on the quantitative milk production in lactating dairy goats indicated almost similar trend of changes in daily milk yield. Therefore, the present similarity in fatty acid composition and slight increase in total unsaturated fatty acids in milk of goats fed 20% SFS ration may indicate the safe use of SFS up to 20% without adversely effects on hydrogenation of fatty acids in rumen and consequently marked changes in fatty acid composition in milk fat. The daily milk yield and duration of lactation were individually recorded for goats of each group.
Dietary lipids supplementation, as whole crude oilseeds, may also indeed change fatty acids composition of milk that is one of the most important factors influencing technological and nutritional quality of goat milk (Chilliard et al., 2003). Rate of decline increases with lactation advance up to the attainment of minimal milk yield values when goats are dried up (Mbayahaga et al., 1994). Ultimately, one of the main incentives for pursuing these goals is likely to be the need to reduce the risk of losing the entire herd. These results are similar to those reported by Otaru et al., (2011) on goats fed fat supplemented diets.
While, negative regression coefficients of fat on total milk yield were found in Jamnapari goats (Pal et al.



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