The impact of beef sire breed on dystocia, stillbirth, gestation length, health, and lactation performance of cows that carry beef × dairy calves.

In the United States, it is becoming common for dairy herds to mate a portion of cows to beef semen to create a value-added calf. The objectives of this study were to determine if dystocia risk, stillbirth (SB) risk, gestation length (GL), probability of early-lactation clinical disease events, early-lactation culling risk, or subsequent milk production differ between cows that carried calves sired by different beef breeds and those that carried Holstein-sired calves. Records from 10 herds contained 75,256 lactations from 39,249 cows that had calves with known Holstein or beef breed sires from the years 2010 to 2023. Calf sire breeds with ≥150 records included in analyses were Holstein, Angus, Simmental, Limousin, crossbred beef, and Charolais. Additional beef sire breeds that existed in lower frequency (n < 150 records) were condensed together and classified as "other." Because GL is a continuous variable, sire breed inclusion criteria were reduced to n ≥ 100 records; thus, Wagyu sires were included as their own breed group. Some records did not contain all variables of interest, thus models included fewer lactations depending on variable. Binomial generalized mixed models evaluated dystocia risk (defined as calving ease score ≥4 or calving ease score ≥3), SB risk, clinical health event risk (defined as lameness, mastitis, metabolic, reproductive, other, or any health events occurring within 60 d in milk [DIM]), and early culling risk (defined as death or culling within 60 DIM). Gestation length and test-date milk, fat, and protein yields were evaluated with mixed models. Calves sired by crossbred beef bulls had a greater probability of being stillborn (5%; 95% confidence interval lower = 2.9% upper = 9.0%) than those sired by Holstein bulls (2%; 95% confidence interval lower = 1.5%, upper = 2.7%). All beef-sired calves increased GL from that of Holstein-sired calves (277 ± 0.15 d) with Limousin (282 ± 0.81 d) and Wagyu-sired calves (285 d ± 0.79) resulting in the longest GL. The risk of dystocia, clinical health events, and early-lactation culling did not differ by calf sire breed nor did subsequent milk and component yield. Generally, carrying a calf sired by the beef breeds included in this study did not negatively affect the dairy cow.

Genetic parameters and genomic regions associated with horn fly resistance in organic Holstein cattle.

Horn flies (Haematobia irritans [L.]) contribute to major economic losses of pastured cattle operations, particularly in organic herds because of limitations on control methods that can be used. The objectives of this research were to determine if resistance to horn flies is a heritable trait in organic Holstein cattle, determine associations with yield traits, and to detect genomic regions associated with fly infestation. Observations of fly load were recorded from 1,667 pastured Holstein cows, of which 640 were genotyped, on 13 organic dairies across the United States. Fly load score was determined using a 0 to 4 scale based on fly coverage from chine to loin on one side of the body, with 0 indicating few to no flies and 4 indicating high infestation. The scoring system was validated by counting flies from photographs taken at the time of scoring from 252 cows. To mitigate the effect of our data structure on potential selection bias effects on genetic parameter estimates, survival to subsequent lactations of scored animals and herd-mates that had been culled before the trial was accounted for as the trait stayability. Genetic parameters were estimated using single-step genomic analysis with 3-trait mixed models that included fly score, stayability, and a third phenotype. Model effects differed by variable, but fixed effects generally included a contemporary group, scorer, parity, and stage of lactation; random effects included animal, permanent environment, and residual error. A genome-wide association study was performed by decomposing estimated breeding values into marker effects to detect significant genomic regions associated with fly score. The rank correlation between the subjective fly score and the objective count was 0.79. The average heritability of fly score (± standard error) estimated across multiple models was 0.25 ± 0.04 when a known Holstein maternal grandsire was required and 0.19 ± 0.03 when only a known Holstein sire was required. Genetic correlation estimates with yield traits were moderately positive, but a greater fly load was associated with reduced yield after accounting for genetic merit. Lower fly loads were associated with white coat coloration; a significant genomic region on Bos taurus autosome 6 was identified that contains the gene KIT, which was the most plausible candidate gene for fly resistance because of its role in coat pattern and coloration. The magnitude of heritable variation in fly infestation is similar to other traits included in selection programs, suggesting that producers can select for resistance to horn flies.

Cholesterol deficiency carriers have lowered serum cholesterol and perform well at an elite cattle show.

Cholesterol deficiency (CD) in Holstein cattle results from an insertion in the APOB gene, which traces to the bull Maughlin Storm and was spread to elite show cattle largely through his grandson Braedale Goldwyn. Calves that are homozygous for CD can neither transport dietary fat from the gut nor synthesize low-density lipoproteins, and they perish before 6 mo of age. The mutation may have a partially dominant effect, with lowered cholesterol in heterozygous animals. Our aims were to evaluate serum cholesterol in heterozygous animals, evaluate daily phenotypic records of lactating CD carriers, and determine whether CD carrier status is associated with show ring success. Blood was collected on a single date in May 2018 from 12 carriers and 14 controls and 1 yr later from 17 carriers (7 repeated for 2018) and 27 controls (6 repeated from 2018); animals ranged in age from 14 to 84 mo and varied in stage of lactation and pregnancy status. Serum samples were analyzed for cholesterol concentration (mg/dL) and results were analyzed using mixed models that included linear and quadratic effects of days in milk and days carried calf. Daily phenotypic records of milk yield, milking time, milk conductivity, activity, and body weight were compared between carriers and controls. Additionally, the CD carrier status of cows that were sired by known CD carriers and had available genotypes was recorded. Cows placing in the top 5 and top 10 of their classes at World Dairy Expo between the years of 2006 and 2019 were included in our analysis. Chi-squared tests for equal proportions were evaluated to determine whether the following were associated with CD status: placing in the top 10 with repeated placings from the same cow included, placing in the top 5 with repeated placings, top 10 cows considering individuals only once, and top 5 cows considering individuals only once. Control animals (noncarriers) had significantly higher serum cholesterol (116.21 ± 6.45 mg/dL) than CD carriers (90.15 ± 7.49 mg/dL). There was no difference between carriers and controls in milk yield, milk conductivity, or activity. However, CD carriers had shorter milking times and lower body weights than their herdmates. Further, there were more CD carriers in the top 5 and more carriers tended to place in the top 10 at World Dairy Expo when repeated placings were included. These data support observations that CD is partially dominant and indicate that CD carriers display other phenotypic differences from their herdmates that may give them a small advantage at elite cattle shows.