-The objective of this study was to investigate changes in physiological parameters of dairy cows and understand which physiological parameters show greater reliability for verification of heat stress. Blood samples were collected for analysis and included hematocrit (Ht), erythrocyte count (ERY), and hemoglobin count (HEMO). In addition, physiological variables, including rectal temperature (RT), heart rate (HR), respiratory rate (RR), and panting score (PS) were recorded in 38 lactating cows. These varied according to genetic group (½, ¾, and pure bred Holstein (HO)). Analysis of variance considering the effects of genetic group, days, and their interaction as well as linear and quadratic effect of the black globe humidity index (BGHI) was performed, as well as broken-line regression. These values were higher in pure HO than in ¾ and ½ groups. The average BGHI during the morning was 74, when 70, 43, and 13% of pure HO, ¾, and ½, respectively, presented RR above reference value. The RR was the best indicator of heat stress and its critical value was 116 breaths/min for ½, 140 for ¾, and 168 breaths/min for pure HO cows. In the HO group, physiological variables increased linearly with BGHI, without presenting inflection in the regression. The inflection point occurred at a higher BGHI for the ½ group compared with the other groups. Hematocrit and HEMO were different among genetic groups and did not vary with BGHI, showing that stress was not sufficient to alter these hematological parameters. The ½ HO group was capable of maintaining normal physiological parameters for at least 3 BGHI units above that of HO and 1 to 3 units higher than ¾ HO for RR and RT, respectively. Respiratory rate is the physiological parameter that best predicts heat stress in dairy cattle, and the 1/2 Holstein group is the best adapted to heat stress.

-The objective of this study was to determine whether infrared thermography is a useful tool for the recognition of dairy cows in a state of thermal heat stress, as well as to identify the best region of the animal to be evaluated for this recognition. Physiological variables, including rectal temperature, respiratory frequency, cardiac frequency, and panting score were recorded in 38 lactating cows. For the assessment of environmental parameters, a digital black globe thermometer (TGD-200 model) was used. Thermographic photographs of different regions of the body of cows were taken using an infrared camera (FLIR ® System T300) and indicated respective superficial temperature. Physiological variables and superficial body temperature in different regions varied between genetic groups (Girolando: ½ Holstein × ½ Gir and ¾ Holstein × ¼ Gir; purebred Holstein). The environmental temperature ranged from 20.7 to 37.9 °C with a relative humidity reaching 95%. The mean rectal temperature (40.84 °C), respiratory frequency (111.36 breaths/min), and cardiac frequency (99.22 beats/min) were higher for pure Holstein than for Girolando cows. Positive correlations were found between the physiological parameters and thermographic measures. The highest positive correlation (0.74) was found between the temperature in the lateral region of the udder and rectal temperature. Thermography is a good indicator of thermal comfort. The best region to identify heat stress in cows using thermography is the lateral region of the udder.

Dairy cattle raised under harsh conditions have to adapt and prevent heat stress. The aim of this study was to evaluate physical characteristics and their association with heat tolerance in different genetic groups of dairy cattle. Thickness of the skin and coat, length and number of hairs, body measurements, as well as physiological parameters and body temperatures by infrared thermography were determined in 19 Holstein and 19 Girolando (½ and ¾ Holstein) cows. The Holstein cattle were less tolerant to heat stress than Girolando (GH50 and GH75 Holstein), because of the difficulty in dissipating heat due to the larger body size, as well as thicker and longer hairs. The correlations between physical characteristics, physiological parameters, and thermographic measurements prove to be inconsistent among genetic groups and therefore are not predictive of heat tolerance, while the regressions of morphometric characteristics on physiological and thermographic measures were not significant. Thus, the physical characteristics were not good predictors of physiological indices and thermographic temperature and so should not be used.

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-This study aimed to estimate heritability, genetic, and residual correlations between reproductive traits such as age at first calving, calving interval, dry period, and first service period and linear type traits measured in Holstein cows born between the years 1990 and 2008 in Brazil. The (co)variance components were estimated by restricted maximum likelihood, using the MTDFREML software. The heritability for reproductive traits and linear-type traits ranged from 0.02 to 0.03 and from 0.07 to 0.40, respectively. Estimates of genetic correlations between reproductive and linear-type traits ranged from -0.23 (top line) to 0.28 (angularity) to age at first calving, from -0.54 (final score) to 0.34 (foot angle) to calving interval, from -0.23 (angularity) to 0.56 (stature) to dry period, and from -0.52 (final score) to 0.36 (height udder) to first service period. Direct selection for any of the reproductive traits implies low genetic gains by virtue of their low heritabilities. Among the linear-type traits, the final score, chest width, top line, angularity, teat length, udder attachment, rear teat placement were highlighted as good auxiliary traits to improve reproductive efficiency of Holstein cows in Brazil. The simultaneous selection for reproductive and linear-type traits can lead a higher genetic progress in the reproductive traits.Key Words: age at first calving, dairy cattle, genetic parameters, reproductive efficiency Revista Brasileira de Zootecnia

The objective of this work was to evaluate the effects of breed and heterosis on the estimates of genetic parameters of 305-day milk yield (305MY), by fitting milk yield data to the Wood, Mixed Log, Morgan, and Wilmink non-linear models. A total of 258,891 test-day milk yield records of 37,965 Holstein (H), Gyr (G), and Girolando (1/2 H, 1/4 H, 3/4 H, 3/8 H, 5/8 H and 7/8 H genetic groups) cows from 1840 herds were collected in the state of Minas Gerais, Brazil, in the period of 1998 to 2014. The pedigree file included 36,640 animals, 3677 bulls and 24,472 cows. The genetic parameters were obtained by one-character analysis using the AIREMLF90 software. The heritability estimates of 305MY, and of 305MY fitted to the different nonlinear models ranged from 0.14 to 0.20. Most genetic groups had heterosis effect, with the greatest effects for 305MY on 1/2 H (1/2 Holstein  1/2 Gyr) cows, presenting a milk yield of 1112.73 kg higher than the average of their parents. The results indicate that most genetic groups of Girolando present heterosis effect for 305MY estimated through nonlinear models, and the possibility of obtaining moderate genetic gains when these animals are subjected to selection procedures. HIGHLIGHTS The use Girolando cows in production systems in Brazil has shown positive results of production. This greater productive efficiency may be because of heterosis on the production and adaptation of these animals. The effect of breed and heterosis can be included in traditional models for the improvement of selection.

Breeding and genetics Full-length research article Inbreeding depression in Holstein cattle in Brazil ABSTRACT-The objective of this study was to evaluate inbreeding depression in Holstein cows in Brazil, considering their 305-day milk production (MP), age of first calving (AFC), and calving interval (CI). The effects of inbreeding depression on the traits were determined using four regression models (linear, quadratic, exponential, and Michaelis-Menten) about the errors generated by the animal model. The linear model was significant for CI, and the quadratic model was significant for CI and AFC. The Michaelis-Menten and exponential models were significant for MP, AFC, and CI. Inbreeding depression affected MP and CI. Cows with inbreeding coefficient of 15% produced approximately 260 kg less milk than non-inbred cows. A 1% increase in the inbreeding level resulted in an unfavorable increase of CI of 1.88 days. The quadratic and exponential models showed no variations for CI with increasing inbreeding level; however, the Michaelis-Menten model showed a positive effect of inbreeding on CI. Despite of the small number of inbred Holstein cows, the inbreeding negatively affected milk production and calving intervals. Therefore, breeders should monitor their cattle inbreeding levels. The Michaelis-Menten and exponential non-linear models are best suited to fit inbreeding data of Holstein cows.

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