D.L. Thomas

Genetic variation of lactation curves in dairy sheep: a Bayesian analysis of Wood’s function

Abstract Test-day milk yield records (1752) of 451 first-lactation ewes in four flocks from Nebraska and Wisconsin were analyzed. Breeds included crosses among Dorset, Romanov, Targhee, Rideau Arcott, Polypay, Booroola Merino, Suffolk, Rambouillet, Finnsheep and East Friesian. The objective was to investigate genetic variation of features of lactation curves using a three-stage Bayesian hierarchy. Wood’s model, E ( y | a , b , c , t )= at b exp(− ct ), was used as first-stage; a indicates level of starting yield, and parameters b and c describe ascending and descending phases of the lactation curve; t is time. The second-stage model described variation between ewes. It had a linear structure including flock-year, age at lambing, type of lambing, length of suckling period and the expected percentage of genes of East Friesian origin as fixed effects, plus random additive genetic effects. The third stage included prior distributions for all unknown parameters. Gibbs sampling and the Metropolis–Hastings (MH) algorithm were employed for drawing samples from posterior distributions of parameters. A chain of 60 000 iterations (burn-in of 11 000) was used. Acceptance rate with MH was 24%. Residual variance (posterior mean) was 0.042 kg 2 . Posterior means of heritability of a , b and c were 0.35, 0.35 and 0.27, respectively. Estimates indicate that part of the variation in lactation curves between ewes is heritable. Genetic correlations were negligible, suggesting flexible scope for modifying lactation curves via genetic selection

Udder measurements and milk production in two Awassi sheep genotypes and their crosses

To improve the effectiveness of community-based breeding programs for increased milk production, the values of different udder measurements for predicting milk production traits during the milking period were assessed over 3 yr on 273 Awassi ewes. Machine milking of ewes began after weaning, 56 d after parturition, and continued until the milk yield of the ewes was <200 mL/d. Milk yield obtained by hand milking and milk composition were measured weekly, and days in milk, total milk yield, and total yields of protein, fat, and nonfat solids in milk were calculated for each ewe. On d 70 of milking, morphological traits of the whole udder (circumference, width, height, and length), udder cistern (height), and teats (length, width, and position score) were measured. On the same day, the milk yield of ewes was recorded by hand milking. Positive and moderate to strong correlations (r = 0.36 to 0.76) between udder circumference and width, teat width, and milk production traits of total milk yield, and total yields of protein, fat, and nonfat solids were found. However, a more accurate predictor of milk production traits was milk yield on d 70, as higher positive correlations between this variable and the milk production traits were found (r = 0.63 to 0.89). Nine farmers were invited to independently estimate the hand-milked milk yield performance of a sample of 169 ewes (d 15 to 45 of milking) by visually observing each ewe and making a subjective linear score (1 to 5). Their assessments were significantly correlated with milk yield on the day of the observation (r = 0.52), total milk yield (r = 0.50), and days in milk (r = 0.45). Considering the perception details provided by farmers concerning each of the subjective linear scores, it was found that most predictive linear udder measurements of udder circumference and width and teat width identified in this study were implicit in these scores. The predictive ability of the measurements studied have practical implications for community-based breeding programs involving improvement of milk production-not just in Syria, but in other countries in dry areas as well-because it is possible for experienced farmers to visually assess milk production of dairy ewes or take simple udder measurements with predictive value.

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.

Effect of rumen-undegradable protein supplementation and fresh forage composition on nitrogen utilization of dairy ewes1

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.

Performance and utilization of Northern European short-tailed breeds of sheep and their crosses in North America: a review.

The five Northern European short-tailed sheep breeds present in North America are the Finnsheep, Romanov, Icelandic, Shetland and Gotland. The Finnsheep and Romanov were first imported in 1966 and 1986, respectively, for their high reproductive performance. The Shetland, Icelandic and Gotland breeds were first imported in 1980, 1985 and 2005, respectively, for the uniqueness of their physical appearance and their unique fleeces desired by fiber craftspeople. There have been no scientific studies conducted on the performance of the Shetland, Icelandic or Gotland breeds relative to other breeds of sheep in North America. However, the Shetland and Icelandic breeds have become very popular in the United States and ranked 9th and 18th, respectively, among 35 breeds of sheep for number of purebred animals registered in 2008. The performance of the Finnsheep breed in North America relative to domestic breeds has been thoroughly investigated. Compared to several domestic purebreds and crosses, sheep with Finnsheep breeding had a younger age at puberty, greater fertility to autumn mating, greater litter size, greater survival to weaning, similar growth rate, similar subcutaneous fat thickness, smaller loin muscle area and greater percentage of kidney and pelvic fat. Each 1% increase in Finnsheep breeding in ewes was associated with approximately 0.01 more lambs born per ewe lambing. In North American studies, Romanov ewes were superior to Finnsheep ewes for reproductive rate and lamb production per ewe under both autumn and spring mating. Lambs of the two breeds were similar for survival, growth and carcass traits. Romanov and Romanov-cross ewes produced fleeces that were heavily contaminated with medulated and colored fibers and were of very low commercial value. Three composite breeds containing 25% to 49% Finnsheep breeding (Polypay, Rideau Arcott and Outaouais Arcott) were developed in North America and are now more popular than the Finnsheep breed.

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.

Ewe productivity of Booroola Merino–Rambouillet crossbred sheep during early stages of the introgression of the FecB allele into a Rambouillet population

Productivity of F1 Booroola Merino (BM)×Rambouillet (R) ewes, ewes from the first and second backcrosses to R rams, and purebred R ewes were compared during the early stages of an introgression scheme to introduce the FecB allele into the R population. Fec genotype was estimated by counting corpora lutea during a laparoscopic examination of a ewe’s ovaries at 17 to 19 months of age. One copy of the FecB allele increased (P<0.001) ovulation rate by 1.6 ova per ewe and prolificacy by 0.65 lambs born per ewe lambing. The BM crossbred ewes were 11 kg lighter than R ewes (P<0.001) at breeding. Ewes of FecB+ genotype produced lambs with lower (P<0.001) live weights than did ewes of Fec++ genotype with the differences ranging from −1.4 kg at birth to −5.6 kg at 120 days of age. Lambs from FecB+ ewes had approximately 15% lower (P<0.001) survival than did lambs from Fec++ ewes. Higher reproductive performance of FecB+ ewes was counteracted by poorer growth and survival of their lambs resulting in no difference between Fec genotypes for total weight of lamb produced per ewe to 30, 60, or 120 days postpartum.

Genetic variation of lactation curves in dairy sheep: quadratic function versus Wood’s model

Abstract Daily milk yield records (1752) of 451 first-lactation ewes in four flocks from Nebraska and Wisconsin were analyzed. Most ewes did not have test-day records prior to day 30, and milk yield was recorded more frequently in the second half of lactation. Objectives were to investigate genetic variation of features of lactation curves using a quadratic function (Q), and to compare this with non-linear Wood’s model (W). A three-stage Bayesian hierarchical model was used. At stage 1 of Q, the function y = a + bt + ct 2 + e represented within-ewe variation, where t is time. The stage 2 model described variation in a , b and c between ewes. It had a linear structure with flock-year, age at lambing, type of lambing, length of suckling period and percentage of East Friesian origin genes as fixed effects, and additive genetic effects as random. Stage 3 had prior distributions for all unknowns. A chain of 70,000 iterations (burn-in=12,000) was generated using Gibbs sampling. Posterior means of the residual variance were 0.0234 kg 2 for Q and 0.042 kg 2 for W. Heritabilities of a , b and c in Q were 0.23, 0.15 and 0.17, respectively. Genetic correlations between parameters in Q ranged between −0.51 and −0.36. Q had an R 2 =0.92, higher than the 0.74 found for W. The log-Bayes factor for Q relative to W was 11.64, strongly favoring the quadratic model. Using three residual standard deviations as cut-off, the percentages of outliers were 0.2 and 0.4% for the Q and W models, respectively. Both models fitted well, but Q failed to predict total milk yield accurately. Although model W is more appealing than Q, because its parameters have a mechanistic interpretation, it was not well supported by the data.

Organization and funding of sheep research and extension in the United States — from research to practice

Abstract The generation of sheep research results and the transfer of these results into practice on sheep farms in the U.S. is accomplished through the cooperative funding of sheep research and extension by Federal, state, and local governments and the complete integration of the extension service and research scientists within Land Grant Universities. Over

Effects of service sire on prenatal mortality and prolificacy in ewes.

40 million is spent annually on 800 to 1000 sheep research projects conducted at United States Department of Agriculture, Agricultural Research Service stations and at Land Grant Universities. State Sheep Extension Specialists and County Extension Agents interact directly with research scientists and assist sheep producers in the transfer of research results into practice. Sheep producers provide few funds for sheep research, but through their national organization, the American Sheep Industry Association, support valuable educational functions and influence sheep research and extension activities conducted by public institutions. However, sheep research receives the smallest amount of funding of any of the livestock sectors — only 47% as much as poultry which receives the second lowest amount of funding and 24% as much as beef cattle which receives the largest amount of funding. As a result, fewer scientists are involved in sheep research at each institution than in research with other livestock species, and some important areas of research are not addressed. By necessity, several informal arrangements of sharing scientific expertise among institutions in different states have evolved between sheep scientists, but there is now a need to formalize such arrangements in order to gain the most benefit out of limited sheep research and extension resources.