Effect of calves’ supplementation on performance, nutritional and behavioral characteristics of their dams

The effects of supplementation of beef calves on weight gain, intake and digestibility of pasture, milk production and composition of their dams, and behavior of the pair cow–calf were assessed. Fifty-five beef cows with an initial average body weight of 449?±?8 kg and their respective offspring, with an initial average body weight of 138?+?3 kg and aged between 90 and 150 days, were used. Animals were submitted to an experimental period of 112 days. The experimental treatments consisted of: control?=?mineral mixture only, plan 1?=?high protein and high carbohydrate multiple supplement, plan 2?= high protein and low carbohydrate multiple supplement, plan 3?=?low protein and high carbohydrate multiple supplement, and plan 4?=?low protein and low carbohydrate multiple supplement. About 25 and 12.5 % of the protein requirements were supplied by the high and low protein supplements, respectively, and 15 and 7.5 % of total digestible nutrient requirements by the high and low carbohydrate supplements, respectively. Grazing behavior, performance, milk production, milk composition, intake, and digestibility of the cows were not affected (P?>?0.05) by the supplementation of the calves. The supplemented calves had greater (P?<?0.05) performance (as measured by final body weight, average daily gain, and final body condition score), intake and idle time, and lower (P?<?0.05) grazing time, but supplementation did not affect (P?>?0.05) suckling time and suckling frequency. It can be concluded that supplementation affects the behavior and feed intake of calves. However, it does not affect the suckling time and suckling frequency of calves. Additionally, performance, milk production, nutritional characteristics, and behavior of their dams are not affected.     

Lymphoid leukosis viruses,their recognition as ‘persistent’ viruses and comparisons with certain other retroviruses of veterinary importance

Diseases caused by lymphoid leukosis virus (LLV), a retrovirus, take a long time after infection to develop and have a wide variety of pathological manifestations. This long latent period is characteristic of persistent virus infections. Disease produced by LLV infection and its underlying mechanisms is compared with persistent infections caused by other retroviruses in birds and mammals of veterinary importance. The diseases considered for comparison are those caused by reticuloendotheliosis, feline leukaemia, bovine leukosis and equine infectious anaemia viruses. There are significant changes in the immunological status in all diseases caused by these viruses. LLV infections follow this trend with, in manifestations of neoplastic disease, a perturbation of the normal switch that occurs from IgM to IgG synthesis. There are also indications of other immunological disturbances.Factors other than immunological disturbances may contribute to the length of time after infection required for the many forms of LLV infection to appear. Such additional factors may include the operation of biological clocks, such as the arrival of sexual maturity, and also the very nature of retroviruses. These factors, like the immunological changes, play major roles in the maintenance and progression of persistent retrovirus infections.Abbreviations ACTH adrenocorticotropic hormone - AEV avian erythroblastosis virus - AMV avian myeloblastosis virus - BLV bovine leukaemia virus - CAV chicken anaemia virus - EBL enzootic bovine leukaemia - EIAV equine infectious anaemia virus - env envelope gene - FeLV feline leukaemia virus - FeSV feline sarcoma virus - FOCMA feline oncovirus membrane-associated antigen; gag, group antigen gene - HTLV human T-cell leukaemia virus - LLV lymphoid leukosis virus - L/S leukosis/sarcoma - LTR long terminal repeat - MAV myeloblastosis-associated virus - MDV Marek disease virus - MuLV mouse leukaemia virus - ORF open reading frame; pol, polymerase gene - REV reticuloendotheliosis virus - RIF resistance-inducing factor - RSV Rous sarcoma virus