La fertilité de la vache laitière haute-productrice semble altérée par les teneurs élevées en acides gras (AG) libres du liquide folliculaire observées en début de lactation. Toutefois, les effets diffèreraient selon le type d’AG du microenvironnement de l’ovocyte. La présence d’AG monoinsaturés est associée à des ovocytes ayant un potentiel de développement embryonnaire amélioré. Cette étude visait à évaluer le transfert et l’incorporation des AG alimentaires dans les classes lipidiques du plasma et du liquide folliculaire et son impact sur la fertilité de la vache laitière. Vingt vaches Holstein ont été attribuées aléatoirement à un supplément lipidique alimentaire enrichi soit en acide palmitique (Palmit 80; 82 % 16:0; PA) ou en acide palmitoléique (huile d’argousier; 27 % 16:1 cis-9 et 28 % 16:0; POA). L’administration des traitements (200 g/jour) s’est échelonnée de 20 jours avant à 67 jours après le vêlage. Les performances ont été enregistrées et des échantillons de lait recueillis aux jours 8 à 10 ± 3, 35 à 37 ± 2 et 63 à 65 ± 2 post partum. Aux jours 46 et 67 ± 2 d post partum, les complexes ovocyte-cumulus, les cellules de la granulosa, le liquide folliculaire et des échantillons sanguins ont été prélevés. En comparaison avec PA, POA a augmenté les teneurs en 16:1 cis-9 dans les lipides estérifiés du plasma, dans la matière grasse laitière, et dans les AG libres et les esters de cholestérol du liquide folliculaire. L’expression du gène récepteur à l’insuline tendait à diminuer dans les cellules de la granulosa du groupe POA. Le supplément POA a réduit la folliculogenèse, sans toutefois influencer la compétence au développement des ovocytes. Il est possible de moduler le profil en AG du liquide folliculaire via des stratégies nutritionnelles et de potentiellement influencer le métabolisme des cellules de la granulosa et la folliculogenèse. / In high-yielding dairy cows, fertility is impaired by the increase of non-esterified fatty acid concentrations in follicular fluid during early lactation, but the effects may depend on fatty acid (FA) composition. The objective of this study was to evaluate the potential of dietary supplements enriched in specific FA to influence the FA composition of follicular fluid, and consequently fertility of early-lactation dairy cows. Twenty Holstein multiparous cows in late gestation were randomly assigned to 200 g/d of FA supplements enriched in i) palmitic acid (PA; control treatment; Palmit 80; Natu’oil Services Inc.; 82% 16:0) in the rumen or ii) palmitoleic acid (POA; Sea buckthorn oil; New Directions Aromatics Inc.; 27% cis-9 16:1, 28% 16:0, and 22% cis-9 18:1) in the abomasum. The treatment period ranged from 20 ± 5 d precalving to 67± 2 d postcalving. Performance was recorded, and milk samples collected from days 8 to 10 ± 3 (mean  SD), 35 to 37 ± 2, and 63 to 65 ± 2 postcalving. On days 46 and 67± 2 d postcalving, cumulus-oocyte complexes, granulosa cells and follicular fluid were recovered, and blood was collected. Treatment did not affect milk yield or milk fat. Compared with PA, POA increased cis-9 16:1 concentration in milk fat, in plasma esterified lipid classes, and in follicular fluid non-esterified fatty acids and cholesterol esters. Abundances of mRNA for stearoyl-CoA desaturase and perilipin 2 in granulosa cells were not different between treatments. Moreover, POA treatment tended to decrease the expression of gene encoding for insulin receptor. Treatment did not affect oocyte quality and developmental capacity, or embryo lipid metabolism, but POA altered folliculogenesis. These results suggest that dietary lipid supplements enriched in specific FA may modulate FA profile of the oocyte microenvironment, energy granulosa cell metabolism and folliculogenesis in early lactation cows.

There is growing public concern about the high proportion of saturated fatty acids in milk fat; however, feed intake, energy partitioning toward milk synthesis, and milk fat concentrations can decrease when cows are fed high concentrations of unsaturated lipids. The objective of this study was to identify the optimal rate for feeding OmegaBoostTM (a flaxseed supplement that was processed using a proprietary technique by Double Pass LLC, Tualatin, OR) to dairy cows. The central hypothesis was that supplementation with OmegaBoost will decrease the proportion of saturated fatty acids in milk fat in a dose dependent manner. Using a latin-square design, 10 Holstein cows in mid to late lactation were fed for two-week periods 0, 2, 4, or 6 lbs/d of OmegaBoost or 4lbs/d ground flax as top dressing to their total mixed ration. Feed intake, body weight, activity and resting time, milk production and milk composition were measured daily. At the end of each two-week period, milk and serum samples were taken and analyzed for fatty acid composition using gas chromatography. In addition, fresh Mozzarella cheese and butter was manufactured and tested to determine the fatty acid composition and the effects of flaxseed supplementation on texture. Feeding OmegaBoost at 2, 4, and 6 lbs/d linearly decreased the proportion of saturated fatty acids in milk by 6, 15, and 18%, respectively, and linearly increased the proportion of mono-unsaturated fatty acids (14, 32, and 35%), poly-unsaturated fatty acids (16, 49, and 82%), and α-linolenic acid (26, 52, and 70%). Similar changes in fatty acid composition were observed in butter and cheese samples, resulting in butter that was less hard and adhesive at refrigeration temperature in response to feeding cows increasing concentrations of OmegaBoost. Feed intake, body weight, serum metabolite concentrations, milk production and composition, and butter and cheese yield were not significantly affected by feeding processed flaxseed. Therefore, feeding 4 or 6 lbs/d of OmegaBoost to dairy cows is effective in improving the nutritional and textural profile of dairy products without negatively affecting feed intake, milk production, or weight gain. / Graduation date: 2012

Stearoyl-CoA desaturase1 (SCD1) catalyzes the synthesis of conjugated linoleic acid (CLA) and mono-unsaturated fatty acids (MUFA) in the mammary gland of ruminant animals. We hypothesized that single nucleotide polymorphisms (SNPs) in the coding region, 5' and 3' untranslted regions (UTRs) of the SCD1 gene would influence the activity of SCD1 enzyme and consequently account for some within-breed variations in milk CLA and MUFA. Sequence analysis of the coding region of the SCD1 gene of Jerseys and Holsteins revealed c.702A→G, c.762T→C and c.878C→T SNPs in exon 5 in both breeds and c.435G→A in exon 3 in Holsteins. The SNPs resulted in: A (G435A702T 762C878), A1 (A435A702T 762C878), B (G435G702C 762T878) and B1 (A435G702C 762T878) coding variants in Holsteins and only variants A and B in Jerseys. Only SNP 878C→T resulted in a non-synonymous codon change resulting in p.293Ala and p.293Val protein variants or alleles at the SCD1 locus. Subsequent association studies found significantly higher C10 index, C12 index and C14 index and consequently higher concentrations of C10:1 and C12:1 in p.293AA cows compared to the p.293VV cows in both breeds. The SCD1 genotype had no influence on concentrations of C141, C16:1, C18:1 and CLA in both breeds. / Sequence analysis of the 5' and 3' UTRs revealed no SNPs in the 5'UTR and a total of 14 SNPs in the 3'UTR of both breeds. The SNPs were in complete linkage disequilibrium resulting in 3 haplotypes or regulatory variants: H1 (G1571G1644C1763C2053A2584 A3007C3107G3208 T3290G 3497G3682A4399C4533G4881), H2 (G1571G1644A1763C2053A 2584G3007 C3107G3208T3290G3497G 3682A4399C4533G4881) and H3 (T 1571C1644A1763 T2053G2584G3007T 3107A3208C3290A3497A3682T 4399T4533A4881) in Holsteins and only H1 and H3 variants in Jerseys. A subsequent association study involving 862 Holstein cows, found the H1 regulatory variant to be associated with higher C10 and C12 desaturase indices and consequently with higher concentrations of C10:1 and C12:1 compared with the H3 variant. The effects of the H2 variant were intermediate to those of H1 and H3. 3'UTR genotype had no influence on the concentrations of C14:1, C16:1, C18:1 and CLA. The concentrations of C10:1 and C12:1 in milk fat could therefore be due to effects of SNPs in the open reading frame and the 3'UTR regions of the SCD1 gene. These results indicate that SNPs in the coding and 3'UTR regions of the SCD1 gene could be used as markers for genetic selection for increased C10:1 and C12:1 contents of milk.

MSCAGR (Animal Science) / Department of Animal Science / Milkability, or ease of milking, is the rate at which milk can be completely drawn from a cow’s udder. It is an important functional trait with regard to milking costs as well as udder health. Milkability traits have not been included in the breeding objectives of South African dairy cattle and their genetic parameters in the population have not been estimated. The primary objective of the study was to estimate genetic parameters for milkability traits in South African Holstein cattle. Data consisted of production and milkability records of 1 532 Holstein cows, from 6 herds, participating in the South African National Dairy Animal Recording and Improvement Scheme during the period 2015 to 2016 . Measures of milkability were average milk flow (AMF), maximum milk flow (MMF) and milking time (MT). Genetic parameters were estimated by a multi-trait sire model using the Restricted Maximum Likelihood (REML) procedure. Means for AMF, MMF and MT were 1.99 kg/min, 3.02 kg/min and 5.50 min, respectively. Non-genetic factors affecting variation in milkability traits were herd-year-season of calving, parity and milk yield. Heritability estimates for AMF, MMF, and MT were 0.23±0.09, h2 = 0.41±0.12 and h2 = 0.36±0.11, respectively. Genetic correlations between the three milkability traits were medium to high, ranging from -0.35±0.23 between AMF and MT to 0.79±0.09 between AMF and MMF. Correlations were positive between AMF and MMF and negative between MT and the other two traits. There was an increase in the mean EBV for AMF of 0.002 kg/min (0.0001 kg/min per year) during the period 2002 to 2014. Maximum milk flow also showed an increasing genetic trend of 0.04 kg/min (0.0003 kg/min per year) over the same period. The genetic trend for MT was undesirable, as it increased by 0.0003 kg/min. There is scope for improving milkability through selection, in South African Holstein cattle, as indicated by the moderate to high heritability estimates. The favourable genetic correlations among milkability traits imply that selection on one trait will result in a correlated improvement in the others. Results of the current study provide a basis for including milkability traits in the breeding objective for South African Holstein cattle.

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