Rafael Geraldo de Oliveira Alves

Tendência genética na raça Gir

The importance of weight and weight gain for beef cattle production is responsible for the great emphasis that is devoted to these traits by breeders of different breeds. However, it is very important to maintain the animal breeding programs under surveillance in order to evaluate the genetic progress obtained by a breed as a whole. Thus, this study had the objective of evaluating the genetic trends for gain up to weaning and for gain from weaning to yearling considering the direct genetic and maternal genetic effects for preweaning gain and genetic direct effect for postweaning gain. The genetic trends were estimated by the regression of the annual average expected progeny differences on birth year of the calf. Positive trends were observed for preweaning gain, genetic direct and maternal genetic effect as well. This tendency was also observed for genetic direct effect for postweaning gain. The regression coefficients were 0.19, 0.06 and 0.026 g day-1, for genetic direct and genetic maternal effects for preweaning gain, and for genetic direct effect for postweaning gain, respectively.

Mosca-dos-chifres, Haematobia irritans: comportamento e danos em vacas e bezerros Nelore antes da desmama

The hornfly and losses caused by it in Nellore cows and pre-weaning calves where studied, using two groups of 60 animals each, one group with a natural infestation and the other without hornfly, during four consecutive years. It was seen that the number of flies on the cows did not exceed an average of 80 flies/animal in all years of observation. The majority of the cows (83%) had few flies, whereas 17% had larger numbers. The calves were infested with few flies. Rainfall in excess of 100 mm during short periods diminished fly infestation. Weight gain in the cows without flies (treated with insecticides) as well as their calves was greater than in the control cows, but not statistically significant (P>0.05). Mean percentage pregnancy during the four years was 15% more in treated cows than the non-treated animals, and this difference was probably due to the infestation of the bulls.

Besouros coprófagos (Coleoptera: Scarabaeidae) coletados em Campo Grande, MS, Brasil

Semi-fresh to almost dried cattle dung pats were collected weekly in a pasture of Brachiaria decumbens Stapf, from May of 1990 to April of 1992. The faeces were placed into opaque plastic buckets (15 l) with oppenings at the sides and on the top, occluded with flasks to capture adult coprophagous beetles present in the pats. A total of 18.844 Scarabaeidae specimens were collected, belonging to 37 species of the Genera: Ataenius, Aphodius. Agamopus, Pedaridium, Trichillum, Eurysternus, Dichotomius, Ontherus, Ateuchus, Sulcophanaeus, Gromphas, Digitonthophagus, Onthophagus, and Canthon. Approximately 57% of the species were endocoprids, 35% were paracoprids, and 8% were telecoprids. The most frequent, constant, and abundant species were; Onthophagus hirculus (Mannerheim), Aphodius nigrita (Fabr.), and Ataenius sp.1 (Harold).

Efeito de carrapaticidas/inseticidas "pour-on" sobre adultos do besouro coprófago africano Onthophagus gazella Fabr. (Coleoptera:Scarabaeidae)

In 1989, the dung-beetle Onthophagus gazella Fabr. was imported from the United States to be part of the integrated control program of helminths and horn-fly, Haematobia irritans L. Because there is no information about the effects of pyrethroids on the African beetle survival, the effect of four commercial pour-on insecticides for horn-fly control, on dung-beetle survival was investigated. Fifteen 24 months old, Nelore steers, were randomly assigned to five groups, with three animals/group. Animals in group 1 (control) received no treatment. Groups 2, 3, 4 and 5 were treated on day 0 with Alphamethrin, Cyalothrin, Deltamethrin and Flumethrin, respectively. Individual samples of fecal material (approximately 100 g) were collected from the rectum, on days 1, 4, 8, 11, 15 and 18 after treatment and placed in 500 ml glass vials. Ten live beetles were added in each vial and the survival rate was determined. Beetle mortality was high (P 0,01) in mortality rate among treated groups.

Efeito da mosca-dos-chifres, Haematobia irritans (L.) (Diptera: Muscidae),no ganho de peso de bovinos Nelore

This investigation was carried out due the lack of information about the possible effects of the blood-feeding horn fly, Haematobia irritans (L.), on Nellore cattle. Data were recorded during four rainy seasons (October to April) from 1991 to 1995. In each year, 80 animals were utilized according to the following treatments: twenty-eight 1-year old bulls divided into four groups; twenty 2-year old cattle divided into four groups and thirty-two 3-year old cattle divided into eight groups. Treatments against H. irritans were conduced at about 28-day intervals on half part of each age groups and the remainders groups maintained without treatment as control. The flies were counted at 14-day intervals and the animals weight registered at each 28-day intervals. The values for the mean flies number on the animals of the control groups in the first, second, third and fourth years of this study were: five, five, four and five, in the 1-year old group; 15, 11, 13 and 27, in the 2-year old group, and 55, 31, 40 and 51, in that 3-year old group, respectively. It was observed that higher number of flies (P<0.05) attack adult animals than younger ones. Despite of the low number of flies per cattle, there was a significant weight gain (P<0.05) in favour of treated groups than the controls, which gained 8.6, 16.0 and 10.4% over the period, for groups one, two and three years old, respectively. The weight gain per year was 9, 5, 7 and 8 kg for the 1-year old groups; 26, 10, 23 kg and 12 in 2-year old groups, and 16, 8, 9 and 11 kg in 3-year old groups.

Efeito do tamanho do folículo na maturação nuclear e citoplasmática de ovócitos de fêmeas zebuínas

The objective of this study was to investigate the effect of follicle size on the ability of the oocytes to undergo nuclear and cytoplasmic maturation. Ovaries from Nelore cows (Bos indicus) were collected just after slaughter. The cumulus oocyte complexes were aspirated from four size categories follicles: 1-2 mm, 3-5 mm, 6-8 mm and ³9 mm of diameter. The oocytes were measured and evaluated for chromatin configuration before maturation. After selection the oocytes were matured, fertilized and cultured in vitro. Oocytes obtained from follicles of 1-2 mm showed a smaller diameter (P 9 mm, respectively, showed a germinal vesicle. A similar maturation rate (P 9 mm, respectively. The penetration and clivage rates were also similar (P>0.05) for oocytes obtained from follicle of 1-2 mm (93.4% and 81.9%), 3-5 mm (90.7% and 79.6%), 6-8 mm (91.3% and 77.8%) and ³9 mm (92.0% and 78.3%). In addition, there were no differences (P>0.05) among follicles groups on the percentage of oocytes showing polispermy, decondensed sperm head and pronuclei formation. The results of this experiment showed that oocytes obtained from 1-2 mm to ³9 mm follicles, from Bos indicus, have similar capability to undergo in vitro maturation and fertilization as the larger follicles.

Efeitos genéticos aditivos direto e materno sobre o peso à desmama em animais mestiços Europeu-Zebu

The data used in this study are results of the evaluations of crosses among European breeds and Nellore breed. The data regarding to the weaning weight of 883 calves resulted from six mating groups involving crosses of Simental, Charolais and Chianina breeds with Nellore, backcrosses and pure Nellore, were used. The weaning weights were adjusted for cow and calf ages and contemporary group (formed by the combination of year and season of birth and sex) to estimate direct and maternal genetic additive effects on weaning weight. These effects were estimated by regression of the weaning weight on the individual breed composition, which was considered as a proportion of Nellore genotype. The direct additive effect estimates were 4.43 kg for Simental breed, 6.58 kg for Chianina breed and 15.24 kg for Charolais breed. The maternal additive effect estimates, however, were 41.78 kg for the Simental breed, 26.50 kg for the Charolais breed and 26.11 kg for the Chianina breed.

Disseminação do melhoramento genético em bovinos de corte

With respect to beef cattle breeding, the emphasis devoted by researchers, beef cattle producers and beef cattle experts has been, in general, focused on identification, evaluation and selection of sires. Little attention has been given to the pathway used to spread the genes from such sires throughout the population as a whole. The reported low annual genetic progress observed in several herds might suggest that, in spite of having some success in promoting genetic improvement as observed in isolated herds, such dissemination occurs in a disorganized manner. Such procedure might explain the observed situation where the progress accomplished by some herds is masked by the negative genetic trends observed in others. The theoretical basis of genetic dissemination in beef cattle is reviewed and some theoretical models involving the pyramidal structure of beef cattle production are analyzed, as well as the calculations of the genetic lags involved in each situation.