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    Udder and teat morphology traits associated with milk production and somatic cell score in dairy sheep from a New Zealand flock
    (Taylor and Francis Group on behalf of the Royal Society of New Zealand, 2024) Marshall AC; Lopez-Villalobos N; Loveday SM; Weeks M; McNabb W; Handcock R
    The objective of this study was to estimate the phenotypic correlations between udder and teat morphology traits, milk production traits, and somatic cell score in dairy sheep from a flock in New Zealand. A total of 162 lactating ewes were scored for morphology traits during the milk production season of 2021–2022. The 130-d lactation yields of milk, fat, protein, and lactose were obtained with 2–4 test-days from each ewe and modelled using random regression with orthogonal polynomials. Age had a significant effect on all udder and teat traits. Coat-colour (genetic variety within the breed; white or black) was a significant effect for teat angle and udder separation. Udders that were above the hook were associated with lower milk, fat, protein, and lactose yields. Udders with well-defined separation between halves were associated with higher milk, protein, and lactose yields, and with lower somatic cell count. Well-attached udders were associated with lower fat yield and lower somatic cell score. Teats with a backwards angle were associated with lower milk and lactose yields. Further studies are needed to estimate heritability and genetic correlations between these traits to determine whether these traits should be implemented in breeding programs for dairy sheep in New Zealand.
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    Effect of protein polymorphisms on milk composition, coagulation properties, and protein profile in dairy sheep
    (Elsevier Ltd, 2025-01-01) Marshall AC; Vigolo V; De Marchi M; Lopez-Villalobos N; Loveday SM; Weeks M; McNabb W
    The objective of this study was to quantify the effect of protein polymorphisms on milk composition, coagulation properties, and protein profile in dairy sheep from a New Zealand flock. A total of 470 test-day records, from 147 lactating ewes, were used in the statistical analyses. Protein polymorphisms observed in the RP-HPLC were self-named for purposes of the present study. Data were analyzed using a mixed linear model, including the fixed effects of ewe age, litter size, coat-colour, and stage of lactation, and, as a covariate, deviation from the median lambing date of the flock. The effects of protein polymorphisms were added to the model, one at a time. Protein polymorphisms were significantly (p < 0.05) associated with milk composition and protein profile. Polymorphisms of β-lactoglobulin were significantly associated with milk heat stability, being AB type more heat stable than AA. The other processability traits were not significantly affected by protein polymorphisms. Further studies are required to confirm the protein variants and the properties of individual protein polymorphisms.
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    Genetic evaluation of milk traits, live weight, somatic cell score, and litter size at birth, and development of a selection index for dairy sheep : a dissertation presented in partial fulfillment of the requirements for the degree of Master of Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2016) Scholtens, Megan Rachel
    There is interest in building alternative dairy production systems in New Zealand involving sheep. However, there is currently no national breeding scheme to ensure that genetic change will occur in the right direction. The objective of this study was to develop a prototype genetic evaluation of milk traits, live weight, somatic cell score, and litter size at birth, and a selection index for dairy sheep. The flock consisted of 123 crossbred ewes with a mixture of East Friesian, Highlander, Polled-Dorset and Poltex breeds. A total of 479 monthly flock tests for milk volume and percentages of fat, protein and lactose, and somatic cell count were obtained during the production season 2015-16. Corresponding first let-down time (FLDT) and yields (FLDY) were recorded at afternoon milkings. Ewes were weighed four times during the production season and litter size was recorded at birth (LS). Lactation curves for each ewe were derived using a random regression model with an orthogonal polynomial of 3rd order for fat and lactose daily yields, and an orthogonal polynomial of 4th order for milk and protein daily yields. Average ± SE for lactation length (LL) was 126±4.32 days and averages of accumulated yields were 234±9.10 litres milk, 16.5±0.65 kg fat, 13.0±0.56 kg protein and 12.6±0.48 kg lactose. Average FLDT and FLDY were 79±2.02 seconds and 0.5±0.01 litres, respectively. Averages were 17.5±0.16 for somatic cell score (SCS), 75.9±0.88 kg for live weight (LWT) and LS 2.0±0.06 lambs born per ewe. The coefficient of variation was 38% for lactation length and between 42 and 47% for yields. Breeding values for the different traits were estimated from a multiple-trait animal model using heritability and genetic correlations published in the literature and phenotypic standard deviations obtained from the data set. Economic values (EV) were derived from relative economic weights desired by the famer and genetic standard deviations of the traits. The economic values were $0.516/day for LL, $2.00/kg milk, $6.73/kg fat, $8.37/kg protein, -$0.81/kg LWT, -$46.80/unit of SCS, -$1.80/s of FLDT, $332.30/kg FLDY and $44.00/lamb of LS. It is recommended that the Gunsons use these EVs to calculate a selection index for the ranking of ewes and rams to be selected as parents of the next generation. This will achieve genetic gain for each of the traits in the right direction, in the right proportion as well as producing progeny with improved milk yield, milk quality, milking speed and overall efficiency.