Growth performance of indigenous sheep fed Sporobolus virginicus grass hay grown in saline desert lands and irrigated with high salt content ground water.

Twenty-eight indigenous ewe lambs (6 months of age and 14.4 kg body weight (BW)) were used to evaluate the effect of feeding Sporobolus grass hay (SGH) as the only source of forage on growth, and feed and water intakes. The ewe lambs were randomly and equally allocated to two treatment groups (14 lambs/group). The ewe lambs in group 1 (treatment 1) received SGH, while lambs in group 2 (treatment 2) received Rhodes grass hay (RGH) as the only source of forage. Water was available at all times for both treatment groups. Sporobolus grass was irrigated with brackish water of high salt content (20,000 ppm) and grown in saline desert lands (sabkha) in the United Arab Emirates. The average daily dry matter intake was significantly (P < .05) higher for the animals fed SGH than those fed RGH at all stages. Both water intakes per unit body gain and water intake per unit feed intake were significant (P < .05) between the two treatments group at all stages. Average daily gain did not differ significantly (P > .05) between the two groups at all stages. From these data, we conclude that SGH can replace Rhodes hay in sheep diet without significant effect on sheep performance.

Estimates of genetic parameters for direct and maternal effects on birth weight of local sheep in United Arab Emirates.

Genetic parameters for birth weight were estimated for two sets of purebred and crossbred lambs in United Arab Emirates, using animal model methods. Data were analyzed by restricted maximum likelihood (REML). Five different animal models were fitted. Model 1 considered the animal as the only random effect. Models 2 and 3 included in addition to the additive direct effect of the animal, the additive maternal and the permanent maternal environmental effects, respectively. Model 4 fitted both the additive maternal and permanent environmental effects. Model 5 was the same as model 4, except that a covariance between the direct and the maternal additive effects was included. Estimates of direct heritability were substantially higher when maternal effects were ignored. Introducing the additive maternal effect to model 2 reduced the estimate of additive heritability by 28 and 14% of sigma;(p)(2) for the purebred and crossbred lambs, respectively. Estimates of additive direct and additive maternal heritabilities with model 4 were 0.10 and 0.33, and 0.45 and 0.10 for purebred and crossbred lambs, respectively. The correlation between direct and maternal genetic effects for the combined (purebred+crossbred lambs) data set was large and negative. These results indicate that in addition to additive direct effect, additive maternal effect for birth weight was important.

Response to selection for fertility in a fall-lambing sheep flock.

Selection for fertility in a fall lambing system was applied for 5 yr (1.45 generations) in a crossbred sheep population. Three flocks were involved: a fall-lambing selected (S) flock of 125 ewes and 10 rams, a fall-lambing environmental control (EC) flock of 55 ewes and five rams, and a spring-lambing genetic control flock of 45 ewes and five rams used to produce replacements for EC. Estimated breeding values for fertility (ewes lambing per ewe exposed) were calculated for animals mated in each year of the study using a single-trait animal model and increased more rapidly in S (.0138/yr) than in EC (.0067/yr). After accounting for genetic drift, EBV of ewes mated in S in the final year of the study averaged .070 +/- .032 (P = .08). A correlated response of .0087 lambs/yr was observed in S for fall litter size Genetic trends in all body weights were positive in EC, likely because of supplemental selection on body size in ram lambs used in EC. Ninety-day weight, maternal effects on weaning weight, and 90-d scrotal circumference increased in S, but direct effects on birth and weaning weights declined. In order to focus on realized selection response in fertility, EBV for fertility of 330 replacement ewe lambs from S and EC were calculated using only data collected after their birth. These realized EBV were then regressed on pedigree EBV calculated at the time the ewe lambs were born. The regression was significant when all relationships were used to calculate both EBV (.20 +/- .08) but only approached significance (.13 +/- .07) when only records of the ewe lambs themselves, their descendants, and their paternal half-sibs were used to calculate realized EBV. Also, EBV for all ewes were calculated at the start of each breeding season and were higher (P < .01) for ewes that subsequently lambed than for open ewes. These results suggest that selection can be used to improve fertility in fall-lambing sheep flocks.

Genetic variation and covariation for ewe reproduction, lamb growth, and lamb scrotal circumference in a fall-lambing sheep flock.

Genetic parameters for female reproduction, lamb growth, and lamb scrotal circumference in a composite population of 50% Dorset, 25% Rambouillet and 25% Finnsheep breeding selected for ability to lamb in fall were estimated by REML using various animal models. Traits considered were spring fertility, litter size, weight at weaning (WWT), 90 d (WT90), and 120 d (WT120), and scrotal circumference at weaning (WSC), 90 d (SC90), and 120 d (SC120). Fertility was defined as 1 or 0 for ewes that lambed or failed to lamb, respectively, in fall and averaged .59 for adults (3 yr and older), .45 for second-lambing ewes, .18 for 19-mo-old ewes, and .11 for 12-mo-old ewes. Heritability estimates for fertility varied among models from .07 to .11. Heritability of fall litter size was .10. For body weights, estimates of additive direct, additive maternal, permanent environmental maternal, and litter effects as proportions of phenotypic variance were .04, .10, .05, and .11, respectively, for WWT, .09, .05, .14, and .01 for WT90, and .18, .0, .13, and .06 for WT120. Heritability estimates for WSC, SC90, and SC120 were .15, .25, and .02, respectively. Estimates of genetic correlations among body weights ranged from .77 to unity. Estimates of genetic correlations of fertility with fall litter size, WT90, and SC90 were .56, -.31, and .29, respectively. Genetic correlations of fall litter size with WT90 and SC90 were .33 and .36, respectively. Estimated genetic correlations revealed no major genetic antagonisms with ability to lamb in fall.

Effects of three methods of selection for litter size in mice on pre-implantation embryonic development.

Characteristics of preimplantation embryonic development to Day 3.5 of gestation were evaluated in lines of mice after 21 generations of selection for litter size or components of litter size. Selection criteria were direct selection for number born (LS), selection on an index of ovulation rate and the proportion of ova shed that resulted in fully formed pups (IX), selection for number born in unilaterally ovariectomized females as an indication of uterine capacity (UT), and an unselected control (LC). Comparison of the average distributions of embryonic stage of development on the left side of the uterus showed that selection (average effect of LS, IX, and UT vs. LC) tended to advance (p = 0.07) the average stage of embryonic development at Day 3.5 and shift the distribution (p = 0.10) by increasing the frequency of expanded blastocysts and decreasing the frequency of pre-morula embryos. A similar shift in the distribution on the right side of the uterus was not statistically significant. Selection decreased (p = 0.06) variability in developmental stage among embryos within the right uterine horn. These selection criteria evaluated in the mouse appear to have changed the frequencies of genes that affect some determinants of average stage of embryonic development and uniformity of development within a uterine horn at Day 3.5 of gestation.