Genetic evaluation of semen production potential in Indigenous bulls using random regression models in a Bayesian framework.

Genetic potential of indigenous bulls with respect to semen production traits over the age of the bulls at semen collection was analyzed using random regression models (RRMs). Data pertaining to 59,641 ejaculates from 189 bulls of 18 indigenous breeds collected from BAIF (Bharatiya Agro Industries Foundation) was utilized for this study. Six semen production traits, viz., ejaculate volume (EV, ml), sperm concentration (SC, 109/ml), initial sperm motility (ISM, %), post-thaw motility (PTM, %), the total number of spermatozoa per ejaculate (TNS, 109/ejaculate), and the theoretical number of semen doses (TNSD) were studied. Univariate and RRM were used to obtain variance components and genetic parameter estimates. Two hundred thousand Gibbs samples were generated for each trait with a burn-in of 20,000 and thinning interval of 50 in a Bayesian framework. Legendre polynomials with orders of fit up to 5 for additive and permanent environmental effects were used. RRM modeled the heritability and repeatability for all ages between 3 and 10 years (productive lifespan). Heritability estimates ranged from 0.18 to 0.36, 0.18 to 0.45, 0.02 to 0.06, 0 to 0.001, 0.09 to 0.32, and 0.14 to 0.42 while the repeatability estimates ranged from 0.41 to 0.72, 0.36 to 0.79, 0.04 to 0.10, 0 to 0.001, 0.37 to 0.56, and 0.32 to 0.57 for EV, SC, ISM, PTM, TNS, and TNSD, respectively. Variability of estimates over the age of the bulls obtained through RRM could be useful to further refine the breeding program for age at selection, deciding the production period and age at culling.

Milk yield, composition, and lactation curve models of Bargur cattle under farmers' production system in their native habitat.

Milk yield and composition traits (fat (%) and SNF (%)) from 1229 test day records of 205 Bargur cattle maintained under a farmers' production system were studied. This breed is known for its adaptability to the hilly tracts of Erode District in Tamil Nadu. Performance recording was done in the natural habitat through the test-day milk yield from lactating cows in the farmers' herds. Effects of non-genetic factors like season, year, parity, stage of lactation, and days from calving were studied using mixed models with animal taken as a random effect. Estimated marginal means for daily milk yield (DMY, L/day), fat (%), and SNF (%) were 2.05 ± 0.03, 4.08 ± 0.03%, and 8.19 ± 0.01%, respectively. Stage of lactation was highly significant (P < 0.01) for DMY, fat, and SNF. Season and year were significant for DMY and SNF, where higher productivity was obtained in the monsoon season, but fat remained constant in all the seasons. Parity was significant (P < 0.05) only for SNF, and year was significant for DMY (P < 0.01) and SNF (P < 0.05). Persistency was 5.9% calculated using Wood's gamma function and 63.0% calculated using the ratio of predicted yields. This was slightly lower compared to dairy breeds of cattle. Thirteen different lactation curve models were used for fitting of Bargur cattle lactation curve, and the Parabolic exponential model was the best fitting model based on model diagnostic criteria.