The κ-casein (CSN-3) and β-lactoglobulin (BLG) genes are extensively polymorphic in ruminants. Several association studies have estimated the effects of polymorphisms in these genes on milk yield, milk composition, and cheese-manufacturing properties. Usually, these results are based on production integrated over the lactation curve or on cross-sectional studies at specific days in milk (DIM). However, as differential expression of milk protein genes occurs over lactation, the effect of the polymorphisms may change over time. In this study, we fitted a mixed-effects regression model to test-day records of milk yield and milk quality traits (fat, protein, and total solids yields) from Colombian tropical dairy goats. We used the well-characterized A/B polymorphisms in the CSN-3 and BLG genes. We argued that this approach provided more efficient estimators than cross-sectional designs, given the same number and pattern of observations, and allowed exclusion of between-subject variation from model error. The BLG genotype AA showed a greater performance than the BB genotype for all traits along the whole lactation curve, whereas the heterozygote showed an intermediate performance. We observed no such constant pattern for the CSN-3 gene between the AA homozygote and the heterozygote (the BB genotype was absent from the sample). The differences among the genotypic effects of the BLG and the CSN-3 polymorphisms were statistically significant during peak and mid lactation (around 40-160 DIM) for the BLG gene and only for mid lactation (80-145 DIM) for the CSN-3 gene. We also estimated the additive and dominant effects of the BLG locus. The locus showed a statistically significant additive behavior along the whole lactation trajectory for all quality traits, whereas for milk yield the effect was not significant at later stages. In turn, we detected a statistically significant dominance effect only for fat yield in the early and peak stages of lactation (at about 1-45 DIM). The longitudinal analysis of test-day records allowed us to estimate the differential effects of polymorphisms along the lactation curve, pointing toward stages that could be affected by the gene.

Objetivo. Evaluar la relación de la concentración sanguínea de AMH con el recuento folicular ovárico y la producción in vitro de embriones en hembras bovinas de la raza Brahman. Materiales y métodos. Para estandarizar la técnica de cuantificación de AMH se realizó un primer experimento, en el cual se tomaron muestras de sangre de 10 hembras Brahman sincronizadas en su celo, en tres días diferentes del ciclo estral, con más de 90 días posparto y con evaluación reproductiva normal. La concentración sérica de AMH se determinó con un kit inmunoenzimático comercial. Una vez estandarizada la técnica, se realizó un segundo experimento, se tomaron muestras de sangre de 100 donantes Brahman de ovocitos no sincronizadas, se realizó una sesión de aspiración folicular para la producción in vitro de embriones y se registró el número de folículos mayores de 2 mm en los dos ovarios. Resultados. No hubo diferencias en la concentración de AMH entre los días evaluados del ciclo estral y se encontró una correlación de 0,82 (p<0.001) entre la población de folículos antrales (PFA) y la concentración de AMH. La concentración sérica de AMH osciló entre 0.02 y 2.69 ng/ml. Además, se encontró una correlación de 0.73 (p<0.001) entre AMH y AFP y 0.54 entre AMH y el porcentaje de blastocistos producidos. Conclusiones. La AMH se puede utilizar como un marcador endocrino satisfactorio de la predicción de la reserva ovárica para la producción de embriones in vitro en ganado Brahman.

The Colombian Caribbean dual-purpose livestock system (Bos taurus × Bos indicus) is an important source of milk and beef, yet molecular characterization of trait-associated markers remains limited. This study characterized allele and genotype frequencies of 29 single-nucleotide polymorphisms (SNPs) associated with meat quality and milk production traits in 1585 crossbred heifers from five departments of the Colombian Caribbean. DNA was extracted from hair follicles and genotyped with the Axiom™ Bovine 100K Array. Markers spanned genes for muscle growth and proteolysis (CAPN1, CAST, MSTN), energy metabolism (LEP, DGAT1), and milk protein composition (CSN2, CSN3, PAEP, GH1, GHR, ABCG2). Hardy–Weinberg equilibrium (HWE) was assessed by chi-squared test. Of the 29 markers, 21 were polymorphic and testable: 19 conformed to HWE and 2 deviated (PAEP_239, PAEP_312). The remaining 8 were monomorphic. Approximately 48% of loci showed very high favorable allele frequencies (q > 0.99 or p > 0.99), whereas 52% maintained intermediate heterozygosity. CSN3_526 reached near-fixation of the favorable B allele (q = 0.996), consistent with selection for cheese yield, whereas CAST_282 and CAST_2870 showed high heterozygosity (f(AB) ≈ 0.47–0.48), indicating substantial remaining variation at these loci. These findings provide the first descriptive dual meat-and-milk SNP frequency profile for these crossbred heifers and a molecular baseline for the future development of bioeconomic selection indices in tropical dual-purpose systems. Frequencies are reported at the pooled and department-stratified levels; the results are descriptive and require phenotypic validation before any inference on marker effects or suitability for selection.