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Background: Heat stress derived from global warming is causing major economic losses in the livestock industry. Objective: To develop a novel methodological approach for determining the influence of climatic factors on the estimation of genetic parameters for growth traits in Retinta cattle breed by using reaction-norm models. Methods: Live weight records (n=7,753) from 3,162 Retinta calves born from 1,249 dams and 85 sires and raised in the Andalusian region (Spain) were analyzed. The effect of heat stress was measured using the temperature-humidity index, calculated with climatological data obtained from four weather stations. A bivariate-random-regression reaction-norm model was used to estimate the (co)variance components of weight until weaning in two different climatic seasons corresponding to warm and cold months. Results: The heritability pattern of individuals reared under diverse environments during the first 90 days of age was different. However, differences were not significant at the end of the growing period. Weaned calves reared during the cold season showed greater growth from 70 to 160 days in comparison with those reared during the warm season. Conclusions: Highly significant evidence of genotype-climatic condition interaction was found during the calf's first three months of growth. [ABSTRACT FROM AUTHOR]

Background: Generally, the forages used in cow-calf and backgrounding cattle operations have low crude protein and high fiber concentration, limiting animal performance and increasing greenhouse gas emissions. Chlorella spp., a green microalga, shows promising potential to provide nutrients, especially nitrogen, to low-protein diets. However, information is limited regarding the effects of Chlorella spp. on the in vitro fermentation and methane (CH4) production of diets. Objective: To evaluate the effects of increasing inclusion levels of algae (Chlorella spp.) on ruminal in vitro fermentation profile and CH4 production of a corn silage-based diet. Methods: Incubations were conducted on three separate days using corn silage and gin trash as substrate (70:30 ratio, respectively). Treatments were control (without algae) and 1, 5, and 10% of algae inclusion in the substrate replacing the basal diet. Ruminal fluid was collected from two ruminally cannulated Angus crossbred steers fed ad libitum a corn silage and gin trash diet. Final pH, concentration of volatile fatty acids (VFA) and ammonia nitrogen (NH3-N), in vitro organic matter digestibility (IVOMD), total gas, and CH4 production were determined after 24 h of incubation. Variables were evaluated using the MIXED procedure of SAS software, and means were compared using orthogonal polynomial contrasts. Results: Algae inclusion linearly increased (p<0.01) the IVOMD. However, the final pH and concentration of VFA and NH3-N did not differ (p>0.05) among algae levels. Molar proportion of VFA and the acetate:propionate ratio was not affected (p>0.05) by increasing algae inclusion. Finally, total gas and CH4 production were not different (p>0.05) among treatments. Conclusion: The inclusion of Chlorella spp. does not modify the ruminal in vitro fermentation profile nor the CH4 production of a corn silage-based diet. [ABSTRACT FROM AUTHOR]

Background: The genetic test for Expected Progeny Differences (EPDs) is one of the newest technologies to reduce uncertainty in calf production. It provides information about the genetic composition of a bull, which relates to its propensity to produce offspring with specific growth and quality characteristics. Objective: To evaluate the influence of EPDs reports on the variation of Nellore bull semen prices for artificial insemination in the Brazilian beef cattle industry. Methods: Ordinary Least Squares (OLS) regressions were estimated. The study utilized genetic data provided by GENEPLUS as well as market prices of semen and physical measurements of the bulls collected from the Alta Genetics Insemination Agency. Results: Genetic results, except for age at first calving, weaning weight, and weight at 120 days EPDs, have little influence on semen prices. For each additional day expected for the first calving of the progeny average price of semen decreases by 0.66%. For each additional kg expected in weaning weight, the semen price was 1.73% higher. Furthermore, for each additional kg expected in the progeny at 120 days, semen price increased by 2.46%. Conclusion: Joint analyses of genetic reports and physical characteristics of bulls may provide a better explanatory power. [ABSTRACT FROM AUTHOR]

Background: there is little information in Cuba regarding the genetic components of the postpartum period in beef cattle. Objective: to compare estimates of genetic parameters of days open (DO) obtained with three models in Charolais cattle of Cuba. Methods: data from individual reproductive control of Charolais cattle from 17 herds in two Cuban companies were analyzed. The sample consisted of 16,891 calvings from 4,593 cows, daughters of 190 sires and 2,770 dams. Up to 10 parities per female between years 1981 and 2005 were considered. The WOMBAT program was used to estimate variance components. Three models were applied; an univariate model (UM) for each separate parity until the sixth calving; a repeatability model (RM) with all parities; and a random regression model (ARM) taking the number of calving as an independent variable. Results: the overall average for DO was 171 ± 93 days. The trend of the average value for DO in each calving was decreasing from the first to the tenth parity, with a seasonal performance around 155 days between the fourth and eighth calving. DO heritability estimated by UM was variable, with values of 0.03 for the first calving and 0.06 for the sixth. These variations cannot be observed with RM that estimated a heritability of 0.06. Values of 0.05 in the first calving until 0.07 in the tenth were estimated with ARM. Genetic correlations among DO for different parities were close to unity. Conclusions: changes of the estimated heritability for DO through the productive life of a female can be observed with ARM. The heritability estimates were low and did not differ from the results reported in other beef cattle breeds. [ABSTRACT FROM AUTHOR]

Background: Knowledge of genetic correlations and the economics of traits are essential to decide which traits should be used as selection criteria. Objective: To estimate heritabilities and genetic, environmental, and phenotypic correlations, and direct (DRS) and correlated (CRS) responses to selection by scrotal circumference (SC), frame score (FS), and yearling weight (YW) of Mexican Charolais (CH), and Charbray (CB) young bulls. Methods: Actual SC, height and YW records (10,078 for CH, and 500 for CB) were adjusted to 365 d. The 0.0505 adjustment factor recommended by the Beef Improvement Federation was used to obtain the 365-d adjusted SC for both breeds. Height and age records were used to obtain FS. Data were analyzed using a three-trait animal model. The animal model for each trait included bull breed, contemporary group (groups of young bulls born in the same herd, year, and season of the year), and age of dam as a linear covariate as fixed effects, and direct additive genetic and residual as random effects. Results: Heritability estimates for SC, FS and YW were 0.21 ± 0.04, 0.25 ± 0.04, and 0.29 ± 0.04, respectively. The genetic correlation between YW with SC was 0.37 ± 0.16, and between YW with FS was 0.42 ± 0.16. The estimate of genetic correlation between SC and FS was low and positive (0.15 ± 0.14). The DRS was 0.38 cm, 0.18 units, and 8.30 kg for SC, FS and YW. The CRS was 0.16 cm, and 0.08 units for SC and FS from indirect selection on YW. Conclusions: Direct selection for YW is expected to be effective. Indirect selection for SC and FS based on YW would not be expected to be as effective as direct selection for improving SC and FS. [ABSTRACT FROM AUTHOR]

Background: Nellore cows are well adapted to tropical conditions, and they have good maternal ability as well as long and prolific reproductive life. Objective: to estimate (co)variances and genetic parameters for calving interval (CI), age at first calving (AFC), gestation length (GL), and days open (DO) in Nellore cows. Methods: covariance components and genetic parameters were estimated using multi-trait Bayesian procedures. Results: three traits had low but statistically significant heritabilities, averaging 0.05, 0.10, and 0.04 for CI, GL, and DO, respectively, whereas age at first calving had a higher heritability (0.36). The permanent environmental effects for CI, GL, and DO were also low, averaging 0.08, 0.07, and 0.15, respectively. The genetic correlations between AFC and CI, AFC and GL, AFC and DO, GL and CI, CI and DO, GL and DO were 0.20, 0.12, 0.11, 0.02, 0.92, and -0.21, respectively. Selection for shorter CI would contribute towards decreasing DO. However, selection for decreased GL could result in a greater number of DO. Despite the favorable genetic correlations, the direct selection responses for these traits would be low. Conclusion: reproductive traits are strongly influenced by environmental effects. Changes in management and environmental factors could rapidly improve reproductive performance of Polled Nellore herds. Genetic selection for these traits should produce a much slower but permanent response. [ABSTRACT FROM AUTHOR]

Background: breeding soundness evaluation (BSE) of males is crucial for reproductive success in sheep production systems. Objective: to determine the causes of failure when annual BSE was used to evaluate reproductive performance of rams. Methods: we analyzed 1,017 reproductive assessment records and assigned animals to young or mature groups. Animals were classified as approved or failed in the BSE. Statistical analyses were performed through Chi-square tests, correlation, and factor analyses. Results: our results clearly show the importance of regularly performing BSE to detect potential failures in rams that might reduce general fertility rates. Conclusions: consistent physical causes of failure were identified, and fertility rates varied according to age and year of examination. [ABSTRACT FROM AUTHOR]