Sectional notes

American Journal of Potato Research -     

Growth traits of four maternal lines of rabbits founded on different criteria: comparisons at foundation and at last periods after selection

The objective was to compare growth traits in four maternal lines of rabbits (A, V, H and LP), with the aim of understanding the consequence of the different foundation and selection processes on the growth performance of the lines. The lines are currently in the 43th, 38th, 22th and 8th generations, respectively. Two comparisons were performed. One compared the values of the lines at their foundation, using the complete data set, the full pedigree and a two‐trait analysis, including data on the selection criteria, litter size. The other comparisons were done during the last period when all the lines were housed together with the same feeding and management. The numbers of records were 323 208 for weaning weight, and 300 553 for slaughter weight and average daily Gain (from 46 708 l). The pedigree file included 346 638 animals. The second analysis used only the data corresponding to each period, and the analysis was conducted using a one‐trait model. The model was the same as that defined for the comparisons at the foundation, but the additive effects were excluded. The H and LP lines showed highest values for all the traits compared. In the last periods, a good agreement was observed between the estimated differences, computed with the complete model and data set, or computed with an incomplete model and only data from the comparison period. At last periods, the differences were smaller than at foundation. The importance of the correlated response in growth after selection for litter size at weaning or the importance of a non‐programmed intramating selection for the growth traits can explain the changes since foundation.     

Use of by-products and supplementary protein in dairy cow nutrition

The new systems of protein evaluation distinguish clearly between the requirement of the rumen microbes and the need of the host animal. While the requirement of the rumen microbes and the production of microbial protein is related to fermented energy, the need of the host animal varies with type and level of productivity. In dairy cows microbial protein is insufficient for the host animal, particularly when the animals are in negative energy balance, and in order to efficiently utilise body energy reserves undegraded protein must be given. Several experiments are discussed in which dairy cows have been given ammonia treated straw as the only source of roughage and where milk yields have been maintained. It is emphasised that increased use of high roughage diets in early lactation increases the demand for undegraded proteins. The converse is also true: that undegraded protein increases the proportion of roughage that can be used for high yielding dairy cows.     

The effects of treatments of cecal contents on their protective properties against Salmonella in poults

The effect of manipulating adult turkey cecal contents was assessed. Treatment of day-old poults with cecal contents diluted up to 1/3000 protected 90% of the birds against subsequent challenge with 10(3) colony-forming units of Salmonella typhimurium. The addition of penicillin G and streptomycin to adult cecal contents reduced their protective effects by 20% and 50%, respectively. When cecal contents were heat-treated at 65 C for 15 minutes or filter-sterilized, the protective properties were lost. Anaerobic cultures of cecal contents in reinforced clostridial medium afforded protection against challenge, but protection was lost on subsequent subcultures. Thioglycollate broth culture of cecal contents did not protect.