Fernanda Santos Silva Raidan

Genetic analysis of resistance to ticks, gastrointestinal nematodes and Eimeria spp. in Nellore cattle

The aim of the present study was to obtain genetic parameters for resistance to ticks, gastrointestinal nematodes (worms) and Eimeria spp. in Nellore cattle, analyze the inclusion of resistance traits in Nellore breeding programs and evaluate genetic selection as a complementary tool in parasite control programs. Counting of ticks, gastrointestinal nematode eggs and Eimeria spp. oocysts per gram of feces totaling 4270; 3872 and 3872 records from 1188; 1142 and 1142 animals, respectively, aged 146 to 597 days were used. The animals were classified as resistant (counts equal to zero) or susceptible (counts above zero) to each parasite. The statistical models included systematics effects of contemporary groups and the mean trajectory. The random effects included additive genetic effects, direct permanent environmental effects and residual. The mean trajectory and random effects were modeled with linear Legendre polynomials for all traits except for the mean trajectory of resistance to Eimeria spp., which employed the cubic polynomial. Heritability estimates were of low to moderate magnitude and ranged from 0.06 to 0.30, 0.06 to 0.33 and 0.04 to 0.33 for resistance to ticks, gastrointestinal nematodes and Eimeria spp., respectively. The posterior mean of genetic and environmental correlations for the same trait at different ages (205, 365, 450 and 550 days) were favorable at adjacent ages and unfavorable at distant ages. In general, the posterior mean of the genetic and environmental correlations between traits of resistance were low and high-density intervals were large and included zero in many cases. The heritability estimates support the inclusion of resistance to ticks, gastrointestinal nematodes and Eimeria spp. in Nellore breeding programs. Genetic selection can increase the frequency of resistant animals and be used as a complementary tool in parasite control programs.

Inbreeding on productive and reproductive traits of dairy Gyr cattle

The objective of this study was to estimate genetic parameters and to evaluate the effects of inbreeding on productive and reproductive traits of dairy Gyr cattle. Single-trait animal models were used to estimate genetic parameters and solutions for inbreeding coefficients for milk (milk 305-d), fat (fat 305-d), protein (protein 305-d), lactose (lactose 305-d), and total solids (TS 305-d) yield up to 305 days of lactation, days in milk (DIM), age at first calving (AFC) and calving intervals (CI). The mean inbreeding coefficient was 2.82%. The models with linear and quadratic effects of inbreeding coefficients fitted the data better than the models without or with only linear effect of inbreeding coefficient for all traits. The increase in inbreeding coefficient caused several losses in productive and reproductive traits of dairy Gyr cattle. Estimates of heritability for milk 305-d, fat 305-d, protein 305-d, lactose 305-d, TS 305-d, DIM, AFC, and CI were 0.28, 0.27, 0.22, 0.21, 0.22, 0.17, 0.20, and 0.10, respectively. It is possible to achieve genetic progress in productive traits (especially in milk 305-d and fat 305-d) and age at first calving in dairy Gyr cattle through selection.

Desempenho produtivo e reprodutivo de fêmeas F1 Holandês x Nelogir

It was aimed to evaluate the productive and reproductive traits of 1/2 Holstein x ¼ Nellore, ¼ Gir (Nelogir) females. They were evaluated the effects of order and season of calving, of Gir and Holstein sires grandfathers and fathers of the 1/2 Holstein x Nelogir matrices, respectively. Total milk production, with average lactation length of 288 days, was 3,426.9kg of milk. The order of calving influenced the daily average production which was higher in the second calving and lactation length was superior in the first calving. The beginning of rain period (November to January) showed lower lactation length and production a day of calving interval. Total milk production did not vary according to Gir sire, Nelogir’s father, and was higher in the matrices daughters of Holstein sires with positive PTA for milk. In the first calving the production peak was of 13.03kg at 45 days of lactation, and from the second calving the production was descending one. In tropical conditions, productive and reproductive traits support the initiative of farm animals 1/2 Holstein x Nelogir from matrices composed Nelogir and that the choice of Holstein bull to produce F1 HNG should be based on the genetic value milk production (milk PTA).