Estimates of genetic parameters, genetic trends, and inbreeding in a crossbred dairy sheep research flock in the United States.

For the past 2 decades, the Spooner Agriculture Research Station (ARS) of the University of Wisconsin-Madison operated the only dairy sheep research flock in North America. The objectives of the present study were to 1) obtain estimates of genetic parameters for lactation and reproductive traits in dairy ewes, 2) estimate the amount of genetic change in these traits over time, and 3) quantify the level of inbreeding in this flock over the last 20 yr. Multiple-trait repeatability models (MTRM) were used to analyze ewe traits through their first 6 parities. The first MTRM jointly analyzed milk (180-d-adjusted milk yield [180d MY]), fat (180-d-adjusted fat yield [180d FY]), and protein (180-d-adjusted protein yield [180d PY]) yields adjusted to 180 d of lactation; number of lambs born per ewe lambing (NLB); and lactation average test-day somatic cell score (LSCS). A second MTRM analyzed 180d MY, NLB, LSCS, and percentage milk fat (%F) and percentage milk protein (%P). The 3 yield traits were moderately heritable (0.26 to 0.32) and strongly genetically correlated (0.91 to 0.96). Percentage milk fat and %P were highly heritable (0.53 and 0.61, respectively) and moderately genetically correlated (0.61). Milk yield adjusted to 180 d was negatively genetically correlated with %F and %P (-0.31 and -0.34, respectively). Ewe prolificacy was not significantly ( > 0.67) genetically correlated with yield traits, %P, or LSCS but lowly negatively correlated with %F (-0.26). Lactation somatic cell score was unfavorably genetically correlated with yield traits (0.28 to 0.39) but not significantly ( > 0.09) correlated with %F, %P, and NLB. Within-trait multiple-trait models through the first 4 parities revealed that 180d MY, 180d FY, 180d PY, %F, and %P were strongly genetically correlated across parity (0.67 to 1.00). However, the genetic correlations across parity for NLB and LSCS were somewhat lower (0.51 to 0.96). Regressing predicted breeding values for 180d MY, without and with the addition of breed effects, on ewe year of birth revealed a positive genetic gain of 2.30 and 6.24 kg/yr, respectively, over the past 20 yr in this flock. Inbreeding coefficients of ewes with an extended pedigree ranged from 0.0 to 0.29, with an average of 0.07. To optimize genetic gains and avoid excessive inbreeding, the development of a national genetic improvement program should be a top priority for the growing dairy sheep industry.

Factors affecting ewe performance in a crossbred dairy sheep research flock in the United States.

The Spooner Agricultural Research Station operated the only dairy sheep research flock in North America through 2016. The original nondairy ewe flock was "bred up" to a crossbred dairy flock through the use of rams and semen of the East Friesian (EF) and Lacaune (LA) dairy breeds. The objective of this study was to determine the environmental and nonadditive genetic effects that influence performance of dairy ewes. The traits analyzed were 180 d adjusted milk (180d MY), fat (180d FY), and protein (180d PY) yields, percentage fat (%F) and protein (%P) in milk, lactation average somatic cell score (LSCS), and number of lambs born per ewe lambing (NLB). The univariate repeatability models included the fixed effects of year of lambing, age, weaning system (except for the trait of NLB), individual breed composition, and individual retained heterosis along with the random additive genetic, permanent environmental, and residual effects. Estimates of heritability were moderate for 180d MY (0.32 ± 0.04), 180d FY (0.26 ± 0.04), and 180d PY (0.29 ± 0.04), high for %F (0.54 ± 0.04) and %P (0.61 ± 0.04), and low for LSCS (0.12 ± 0.03) and NLB (0.08 ± 0.02). Ewes that reared their lambs had lower ( < 0.01) 180d MY, 180d FY, 180d PY, %F, and %P and higher ( < 0.001) LSCS than ewes that had their lambs removed shortly after parturition. Relative to nondairy breeding, EF and LA breeding had positive ( < 0.001) effects on 180d MY, 180d FY, and 180d PY, but a negative ( < 0.03) effect on %P. Purebred EF ewes were predicted to have lower ( < 0.001) %F than purebred LA or nondairy ewes. Purebred LA ewes were predicted to have a higher ( < 0.001) LSCS than purebred EF or nondairy ewes. Purebred EF ewes were expected to be more ( < 0.001) prolific than purebred LA or nondairy ewes. Individual retained heterosis had a favorable ( < 0.01) effect on 180d MY, 180d FY, 180d PY, and NLB. Knowledge of the factors affecting dairy ewe performance are important for dairy sheep producers to make more informed husbandry and breeding decisions.

Survival in crossbred lambs: Breed and heterosis effects.

The objective of this study was to estimate genetic and nongenetic effects affecting survival in crossbred lambs during 3 time periods: through 1 d of age ( = 7,933), 2 to 30 d of age ( = 5,370), and 2 to 60 d of age ( = 5,216) in a population being upgraded to the dairy breeds of East Friesian and Lacaune in which lambs were artificially reared on milk replacer. Survival was analyzed for lambs born in 14 yr from 1998 to 2011 using pedigree information from 14,339 animals born in 23 yr from 1989 to 2011. Date of death, sex, age of the dam, birth type, month and year of birth, and breed composition were recorded, and the proportion of retained heterosis was calculated for each animal. Lambs were crossbreds of 2 or more breeds with 14 breeds represented in the population. Due to low mean genetic contribution of the 12 nondairy breeds, they were placed into 2 groups: meat breeds (Hampshire, Suffolk, and Texel) and maternal breeds (Romanov, Finnsheep, Dorset, Targhee, Rambouillet, Polypay, Katahdin, Arcott Rideau, and Commercial). The proportion of individual retained heterosis was positively associated ( < 0.05) with lamb survival from 2 to 30 and from 2 to 60 d of age. The predicted increase in survival of F lambs compared to purebred lambs was +8.8 and +14.6%, respectively. Predicted survival of meat breed lambs and maternal breed lambs was greater ( ≤ 0.01) than Lacaune lambs during all 3 periods. Predicted survival of East Friesian lambs was consistently lower ( ≤ 0.01) than meat breed and maternal breed lambs during all periods. The predicted survival of East Friesian lambs was numerically greater but not significantly different from Lacaune lambs. There was a lower ( < 0.01) survival of females compared to males through 1 d of age (-5.6%), but females had higher ( < 0.01) survival than males in the other 2 periods (2 to 30 d = +3.3% and 2 to 60 d = +6.0%). Through 1 d of age, lambs of triplet and greater birth types had lower ( < 0.01) survival than single lambs (-6.2%), and lambs from 1-yr-old dams had lower ( < 0.01) survival than lambs from 2-yr-old dams (+4.5%). Estimates of heritability of lamb survival were 0.14 (SE = 0.03), 0.03 (SE = 0.04), and 0.06 (SE = 0.03) for the 3 time periods, respectively. An increase in the proportion of individual retained heterosis was the most important genetic factor associated with increased lamb survival in this study.

Effect of rumen-undegradable protein supplementation and fresh forage composition on nitrogen utilization of dairy ewes.

Previous trials with dairy ewes fed stored feeds indicate a positive effect of rumen-undegradable protein (RUP) supplementation on milk yield. However, dairy sheep production in the United States is primarily based on grazing mixed grass-legume pastures, which contain a high proportion of rumen-degradable protein. Two trials were conducted to evaluate the effects of high-RUP protein supplementation and fresh forage composition on milk yield and N utilization of lactating dairy ewes fed in confinement or on pasture. In a cut-and-carry trial, 16 multiparous dairy ewes in mid-lactation were randomly assigned to 8 pens of 2 ewes each. Pens were randomly assigned 1 of 2 protein supplementation treatments, receiving either 0.0 or 0.3 kg of a high-RUP protein supplement (Soy Pass, LignoTech USA Inc., Rothschild, WI) per day. Within supplementation treatment, pens were randomly assigned to 1 of 4 forage treatments, which were applied in a 4×4 Latin square design for 10-d periods. Forage treatments included the following percentages of orchardgrass:alfalfa dry matter: 25:75, 50:50, 75:25, and 100:0. No interactions were observed between supplement and forage treatments. Supplementation with a high-RUP source tended to increase milk yield by 9%. Milk yield, milk protein yield, milk urea N, and urinary urea N excretion increased linearly with increased percentage of alfalfa. Milk N efficiency was greatest on the 100% orchardgrass diet. In a grazing trial, 12 multiparous dairy ewes in mid lactation were randomly assigned to 3 groups of 4 ewes each. Within group, 2 ewes were randomly assigned to receive either 0.0 or 0.3 kg of a high-RUP protein supplement (SoyPlus, West Central Cooperative, Ralston, IA) per day. Grazing treatments were arranged in a 3×3 Latin square design and applied to groups for 10-d periods. Ewes grazed paddocks that contained the following percentages of surface area of pure stands of orchardgrass:alfalfa: 50:50, 75:25, and 100:0. No interactions were found between supplement and forage treatments. Milk yield, milk protein yield, and milk urea N increased linearly with increased percentage of alfalfa in the paddock. In conclusion, supplementing with high-RUP protein tended to increase milk yield and increasing the proportion of alfalfa in the diet increased dry matter intake, milk yield, and protein yield of lactating dairy ewes fed or grazing fresh forage.

Effect of protein degradability on milk production of dairy ewes.

The objective of this experiment was to determine the effect of protein degradability of dairy sheep diets on milk yield and protein utilization across 2 levels of milk production. Three diets were formulated to provide similar energy concentrations and varying concentrations of rumen-degradable protein (RDP) and rumen-undegradable protein (RUP): 12% RDP and 4% RUP (12-4) included basal levels of RDP and RUP, 12% RDP and 6% RUP (12-6) included additional RUP, and 14% RDP and 4% RUP (14-4) included additional RDP. Diets were composed of alfalfa-timothy cubes, whole and ground corn, whole oats, dehulled soybean meal, and expeller soybean meal (SoyPlus, West Central, Ralston, IA). Estimates of RDP and RUP were based on the Small Ruminant Nutrition System model (2008) and feed and orts were analyzed for Cornell N fractions. Eighteen multiparous dairy ewes in midlactation were divided by milk yield (low and high) into 2 blocks of 9 ewes each and were randomly assigned within block (low and high) to 3 pens of 3 ewes each. Dietary treatments were arranged in a 3 x 3 Latin square within each block and applied to pens for 14-d periods. We hypothesized that pens consuming high-RUP diets (12-6) would produce more milk and milk protein than the basal diet (12-4) and pens consuming high-RDP diets (14-4) would not produce more milk than the basal diet (12-4). Ewes in the high-milk-yield square consumed more dry matter and produced more milk, milk fat, and milk protein than ewes in the low-milk-yield square. There was no effect of dietary treatment on dry matter intake. Across both levels of milk production, the 12-6 diet increased milk yield by 14%, increased milk fat yield by 14%, and increased milk protein yield by 13% compared with the 14-4 and 12-4 diets. Gross N efficiency (milk protein N/intake protein N) was 11 and 15% greater in the 12-6 and 12-4 diets, respectively, compared with the 14-4 diet. Milk urea N concentration was greater in the 12-6 diet and tended to be greater in the 14-4 diet compared with the 12-4 diet, indicating that the excretion of urea N in this study was more closely related to dietary crude protein concentration than to protein degradability.

Effects of supplementation and stage of lactation on performance of grazing dairy ewes.

The majority of dairy sheep in the world are fed pasture and supplemental grain during lactation; however, no trials have reported the effects of supplementation of dairy ewes grazing improved pastures in North America. In trial 1, 56 three-year-old grazing dairy ewes in early [21 +/- 10 d in milk (DIM)] or late (136 +/- 9 DIM) lactation were fed 0 or 0.82 kg of dry matter/d per ewe of supplement (16.5% crude protein mixture of corn and a soybean meal-based high-protein pellet) in a 2 x 2 factorial arrangement of treatments. There were no significant interactions between stage of lactation and supplementation treatments. Average test-day milk production was higher in early-lactation ewes than in late-lactation ewes (1.74 vs. 1.21 kg/d, respectively). Although test-day milk protein percentage was higher in late-lactation ewes than in early-lactation ewes (5.02 vs. 4.86%, respectively), there was no difference in milk fat percentage between stages of lactation. Supplemented ewes had higher milk production (1.59 vs. 1.36 kg/d, respectively), lower milk fat percentage (5.75 vs. 6.00%, respectively), and lower milk protein percentage (4.84 vs. 5.04%, respectively) than unsupplemented ewes. Milk urea N levels were similar between the 2 stages of lactation and between the 2 supplementation treatments and were above recommended levels for dairy sheep, indicating an excess intake or inefficient utilization of protein for both supplementation treatments. In trial 2, 96 two-, three-, and four-year-old grazing dairy ewes in midlactation (112 +/- 21 DIM) were randomly assigned to 4 treatments of 0, 0.41, 0.82, or 1.24 kg of dry matter/d per ewe of whole corn. Average test-day milk production increased linearly and milk fat percentage decreased quadratically with increasing amounts of corn supplementation. Milk protein yield increased linearly, and milk urea N levels decreased quadratically with increasing amounts of corn supplementation, suggesting an improvement in the utilization of pasture protein with increasing dietary energy intake.

Effect of prepartum photoperiod on milk production and prolactin concentration of dairy ewes.

Long photoperiods during established lactation increase milk production in dairy cattle and dairy sheep, but recent research in cattle and dairy goats suggests an additional influence of prepartum day length on milk yield in the subsequent lactation. The proposed mechanism of function is the level and role of circulating prolactin in mammary development. The objectives of this study were to evaluate the effect of prepartum photoperiod on milk production, milk composition, and prolactin concentration of 22 multiparous dairy ewes exposed to short day prepartum photoperiod (SDPP; 8 h of light:16 h of dark) or long day prepartum photoperiod (LDPP; 16 h of light:8 h of dark) for at least 6 wk prepartum. During the first 8 wk of lactation, SDPP ewes tended to produce more milk than LDPP ewes (2.43 vs. 2.29 kg/d, respectively), and the milk of SDPP ewes had a greater fat percentage than that of LDPP ewes (6.04 vs. 5.51%, respectively). Due to daily milk yield and greater fat content, SDPP ewes produced more 6.5% fat-corrected milk (+0.30 +/- 0.08 kg/d) and 6.5% fat- and 5.8% protein-corrected milk (+0.28 +/- 0.08 kg/d) than LDPP ewes. For the lactation period of 180 d, SDPP ewes produced more test day milk than LDPP ewes (1.76 vs. 1.60 +/- 0.05 kg/d, respectively), but there were no differences in milk fat or protein percentages. Ewes in both treatments experienced a prolactin surge at lambing, but SDPP ewes had lower circulating prolactin concentration than LDPP ewes from 4 to 0.5 wk before lambing (14.7 vs. 51.3 +/- 4.2 mg/dL, respectively). These data suggest that decreased prepartum photoperiod may be important for increasing milk production in dairy ewes and may provide a management strategy for dairy sheep producers to increase milk yield.

Impact of seasonal changes in ovine milk on composition and yield of a hard-pressed cheese.

A hard-pressed, brined cheese was produced from frozen ovine milk collected in February, May, and August. Solids in the milk decreased as the season progressed. This was a result of high solids in early-lactation milk and low solids in August milk because of hot weather and poorer quality pastures. Casein as a percentage of true protein and the casein to fat ratio were higher in May and August milk. Fat in the cheese from February milk was higher and total protein was lower than in May and August. Milk, whey, and press whey composition were influenced by season and followed the trends of milk composition. Fat recovery in the cheeses ranged from 83.2 to 84.2%. Protein recovery in the cheeses was not affected by season. Cheese yield from February milk was higher than from May and August milk and was a result of higher casein and fat in the milk.

Length of docked tail and the incidence of rectal prolapse in lambs.

A multistate cooperative study was conducted to study the current issue of tail length in docked lambs and its relationship to incidence of rectal prolapse. A total of 1,227 lambs at six locations were randomly allocated to two or three tail dock treatments: 1) short--tail was removed as close to the body as possible, 2) medium--tail was removed at a location midway between the attachment of the tail to the body and the attachment of the caudal folds to the tail, and 3) long--tail was removed at the attachment of the caudal folds to the tail. Short-docked lambs had a greater (P < 0.05) incidence of rectal prolapse (7.8%) than lambs with a medium (4.0%) or a long (1.8%) dock. Female lambs had a higher (P < 0.05) incidence of rectal prolapse than male lambs. At two stations, lambs were finished either in a feedlot on a high-concentrate diet or on pasture with no grain supplementation. At one station, with a very low incidence of rectal prolapse, there was no difference in incidence between lambs finished in the feedlot or on pasture; however, at the station with a relatively high incidence of rectal prolapse, lambs in the feedlot had a higher (P < 0.05) incidence than lambs on pasture. The half-sib estimate of heritability for the incidence of rectal prolapse was low (0.14). The results of this study strongly implicate short dock length as a cause of rectal prolapse in lambs finished on high-concentrate diets. Furthermore, the results of this study and the only other study known conducted on this issue strongly suggest that docking lambs at the site of the attachment of the caudal folds to the tail will result in a negligible incidence of rectal prolapse.

Hard ewe's milk cheese manufactured from milk of three different groups of somatic cell counts.

As ovine milk production increases in the United States, somatic cell count (SCC) is increasingly used in routine ovine milk testing procedures as an indicator of flock health. Ovine milk was collected from 72 East Friesian-crossbred ewes that were machine milked twice daily. The milk was segregated and categorized into three different SCC groups: < 100,000 (group I); 100,000 to 1,000,000 (group II); and > 1,000,000 cells/ ml (group III). Milk was stored frozen at -19 degrees C for 4 mo. Milk was then thawed at 7 degrees C over a 3-d period before pasteurization and cheese making. Casein (CN) content and CN-to-true protein ratio decreased with increasing SCC group 3.99, 3.97, to 3.72% CN, and 81.43, 79.72, and 79.32% CN to true protein ratio, respectively. Milk fat varied from 5.49, 5.67, and 4.86% in groups I, II, and III, respectively. Hard ewe's milk cheese was made from each of the three different SCC groups using a Manchego cheese manufacturing protocol. As the level of SCC increased, the time required for visual flocculation increased, and it took longer to reach the desired firmness for cutting the coagulum. The fat and moisture contents were lower in the highest SCC cheeses. After 3 mo, total free fatty acids (FFA) contents were significantly higher in the highest SCC cheeses. Butyric and caprylic acids levels were significantly higher in group III cheeses at all stages of ripening. Cheese graders noted rancid or lipase flavor in the highest SCC level cheeses at each of the sampling points, and they also deducted points for more body and textural defects in these cheeses at 6 and 9 mo.

Effect of omission of machine stripping on milk production and parlor throughput in East Friesian dairy ewes.

Due to the large cisternal storage capacity and non-vertical teat placement in most dairy ewes, machine stripping is commonly performed to remove milk not obtained by the machine. However, stripping requires individual manual intervention, lengthens the milking routine, and could inadvertently lead to overmilking of other ewes in the parlor. The objective of the present experiment was to estimate the effect of omission of machine stripping on milk production and parlor throughput. East Friesian crossbred dairy ewes that had been machine milked and stripped twice daily from d 0 to 79 postpartum, were randomly assigned to two stripping treatments for the remainder of lactation: normal stripping (S, n = 24), or no stripping (NS, n = 24). The NS ewes yielded 14% less commercial milk during the experiment, but had similar lactation length, milk composition, and somatic cell count compared to S ewes. Average machine milk yield (amount of milk obtained without manual intervention) tended to be greater for NS compared to S ewes. Average machine-on time for S ewes was longer than for NS ewes because of stripping, which may have resulted in over-milking of many ewes in the S group. Results from a milking simulation indicated that parlor throughput would increase by 33%, and overmilking would not occur when stripping was omitted from the milking routine. These results collectively suggest that residual milk left in the udder as a result of omission of machine stripping does not negatively influence milk quality and the loss in commercial milk yield could be compensated for by improved parlor throughput.

Effect of milking interval on alveolar versus cisternal milk accumulation and milk production and composition in dairy ewes.

Cisternal and alveolar milk fractions were measured in East Friesian crossbred dairy ewes (n = 32) after 4, 8, 12, 16, 20, or 24 h of milk accumulation in a 6 x 6 Latin square design by administration of an oxytocin receptor antagonist for recuperation of cisternal milk followed by injection of oxytocin to remove the alveolar fraction. Less than half (38 to 47%) of the total milk yield was stored within the cistern for the first 12 h of udder filling compared with up to 57% after 24 h of udder filling. Subsequent milk yield was significantly reduced following the 16-, 20-, and 24-h treatments. Cisternal milk fat percentage, but not milk protein percentage, was lower than in alveolar milk (4.49 vs. 7.92% milk fat, respectively), indicating that casein micelles pass more freely from the alveoli to the cistern between milkings compared with fat globules. Alveolar compared to cisternal somatic cell count was higher for the 16-, 20-, and 24-h treatments. Significant increases in cisternal milk yield and milk composition observed for the 24-h compared with the 20-h treatment demonstrated the importance of the cistern as a storage space when the alveoli and small intramammary ducts became full. The main difference between cisternal and alveolar milk fractions is the poor fat content of cisternal milk, which is an important reason for the milk ejection reflex to be present during machine milking of dairy ewes. In a second experiment, milking every 16 h compared with every 12 h during mid- to late-lactation did not effect milk yield, milk composition, and quality, or lactation length; however, a 25% savings in labor was achieved with the longer milking interval.

Effect of weaning system on commercial milk production and lamb growth of East Friesian dairy sheep.

East Friesian crossbred ewes (n = 99) and their lambs (n = 232) were used to study the effects of three weaning systems on milk production and lamb growth. Prior to parturition, a ewe and her lambs were assigned to one of the following three treatments for the first 28 +/- 3 d of lactation: 1) ewes weaned from their lambs at 24 h postpartum, ewes machine milked twice daily, and their lambs raised artificially (DY1); or 2) beginning 24 h postpartum, ewes separated from their lambs for 15 h during the evening, ewes machine milked once daily in the morning, and their lambs allowed to suckle for 9 h during the day (MIX); or 3) ewes not machine milked and exclusively suckled by their lambs (DY30). After the treatment period, lambs were weaned from MIX and DY30 ewes, and all three groups were machine milked twice daily. Daily commercial milk yield and milk composition were recorded weekly or twice monthly, and lambs were weighed at weaning or at 28 d and at approximately 120 d of age. Average lactation length (suckling + milking period) was 183 +/- 5 d and was similar among weaning systems. Differences among weaning systems for milk yield, milk fat and protein percentages, and somatic cell count were highly significant prior to and around weaning, and became nonsignificant by 6 wk in lactation. Total commercial milk production was greatest for DY1 and MIX ewes (261 +/- 10 and 236 +/- 10 kg/ewe, respectively) and least for DY30 ewes (172 +/- 10 kg/ewe). Daily gain of lambs to 30 d and weight at 30 d were similar regardless of weaning system; however, by 120 d, DY30 lambs tended to be heaviest, MIX lambs intermediate, and DY1 lambs lightest (47.3 +/- 1.6, 45.9 +/- 1.8, and 43.7 +/- 1.2 kg, respectively). Overall financial returns for milk and lamb sales were greatest for the MIX system because of the increase in marketable milk during the first 30 d of lactation compared with the DY30 system and because of acceptable 120-d lamb weights without the expenses of artificial rearing compared with the DY1 system. A mixed system of suckling and milking during early lactation appears to be a valuable management tool for dairy sheep production.

Comparison of Finnish Landrace and Romanov as prolific breeds in a terminal-sire crossbreeding system.

Targhee ewes lambing to Romanov vs Finnish Landrace rams gave birth to .22 more lambs (P = .02) and had .15 more lambs alive at weaning (P = .11) but did not rear more lambs. Finnish Landrace x Targhee (FT) and Romanov x Targhee (RT) lambs were similar for preweaning survival and for all growth and carcass traits studied. Romanov x Targhee ewes were 14.2 +/- 6.2 d younger (P = .02) at their first estrus and 12.1 +/- 2.8 d younger (P < .01) at their first lambing than FT ewes. The ovulation rate of RT ewes exceeded that of FT ewes by .35 (P < .01). Romanov x Targhee ewes gave birth to .42 more (P < .01) lambs per ewe lambing, had .39 more (P < .01) lambs alive at weaning per ewe lambing, and reared .15 more (P = .03) lambs per ewe lambing than FT ewes. Embryonic survival, adjusted for ovulation rate, was greater (P < .01) for RT (88.3 +/- 3.3%) than for FT (80.0 +/- 3.7%) ewes. Lamb survival was similar for the two F1 crosses, with or without adjustment for number of lambs born. Overall survival (the proportion of ova that resulted in weaned lambs) was greater (P = .02) for RT ewes (77.6 +/- 4.2%) than for FT ewes (67.5 +/- 4.7%), at the same ovulation rate. When ewes were credited with all the lambs they gave birth to, RT ewes produced 4.6 +/- 1.8 kg more (P < .01) weight of lamb at weaning.(ABSTRACT TRUNCATED AT 250 WORDS)

Ram influence on ovarian and sexual activity in anestrous ewes: effects of isolation of ewes from rams before joining and date of ram introduction.

A 2-yr experiment was conducted to determine whether isolation of ewes from rams is necessary to achieve a high response to the ram effect and whether ewes respond as well in May as in June. The experiment was conducted at two locations, with the same four treatments at each location. The four treatments differed with respect to ewe proximity to rams before mating (isolated vs adjacent) and date of joining with novel breeding rams (May 15 vs June 15). The proximity treatment at one location was changed in the 2nd yr; teaser rams were joined with the ewes instead of being adjacent to them. Overall, 86% of the eligible ewes were judged to have responded to the ram effect. A period of isolation before mating did not increase response compared with ewes that remained adjacent to, or in contact with, rams (86 vs 85%). Response was greater (P less than .05) in June and in the 2nd yr (P = .05). A physiological response, different from that generally described, was identified. Ewes ovulated approximately 8 d (8.0 +/- .19 d) after joining with breeding rams. The subsequent ovulation, accompanied by estrus, occurred approximately 15 d later (15.3 +/- .29 d). Eighty-five percent (87/102) of the ewes sampled responded in this manner. However, 82% (31/38) of a sample of these ewes had at least one morphologically normal corpus luteum when examined by laparoscopy 4 d after joining. It seems that these corpora lutea were not completely functional with respect to progesterone production. The ram effect can be achieved without prior isolation of ewes from rams.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic and environmental effects on growth to 1 year and viability of lambs from a crossbreeding study of D'man and Sardi breeds.

Genetic effects were estimated for growth to 1 yr and viability to 90 d of 882 lambs from a diallel cross of Sardi (S), D'man (D), and D'man x Sardi (DS) male and female parents. Sardi direct genetic effects were significantly higher than those of D'man for weights at birth and up to 2 mo, but the difference decreased thereafter and was in favor of D'Man at 6 mo. Sardi maternal ability was better than that of D'man for weights at all ages. Estimates of individual heterosis were small and negative for weight at birth, weight at 1 mo, and lamb viability and positive for other body weights; the estimate was significant for 12-mo weight. Estimates of maternal heterosis were small and did not approach significance for any trait. Epistatic recombination effects were generally small, but negative for all traits and significantly so for viability to 30 d. In general, the results, combined with those on reproduction and total lamb production of ewes of these groups, reported elsewhere, indicate that a population produced by inter se mating of animals 50% D, 50% S breeding is expected to have higher total lamb production than either purebred.