摘要:

Within- and across-country genetic parameters need to be estimated prior to an international genetic evaluation of dairy bulls. A procedure based on the Expectation Maximization algorithm to produce restricted maximum likelihood estimates of such parameters, using national evaluation results from different countries, was tested by simulation. Individual performance records were generated for two populations of dairy cattle with separate breeding programmes but considerable genetic exchange to create ties between the populations. A genotype-by-country interaction effect was generated by simulating the data according to a genetic correlation of 90 between performance in the two countries. Within-country national evaluations were computed with animal models. The estimation procedure was tested using bull national evaluation results. The impact of factors such as data connectedness, time period, and bias in national evaluations on estimated parameters was investigated. When all data were included in the analysis, correct estimates of genetic parameters were obtained. When older data were excluded, within-country variance estimates were biased downwards. When national evaluations of imported bulls, often considered biased owing to preferential treatment of daughters, were excluded, the genetic correlation was underestimated by 12%. When 5-15% bias was introduced into the evaluations of imported bulls in one country and the latter were included in the estimation procedure, genetic correlations were only slightly underestimated. When genetic links between populations were weakened, the genetic correlation was seriously underestimated. A better estimate was then obtained based only on a well-connected subset of the data instead of the entire dataset. The procedure was tested on real data from five countries: Germany, France, Italy, the Netherlands, and the United States of America. Genetic correlation estimates between production traits in these countries ranged from .90 to .97.

ISSN:0906-4702    

DOI:10.1080/09064709609415863

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The present paper describes the effect of heterosis found in a full diallel design 4×4 pure strains of laying hens. There were 36 individually measured hens per combination. In economic terms and with regard to a low food conversion ratio (FCR), positive heterosis was found for egg weight, egg number and total egg mass, while negative heterosis was found for food consumption in the rearing period 0-16 weeks, body weight, weight gain and yolk percentage. On average, there was negative but non-significant heterosis for FCR. Five of the combinations had positive but non-significant heterosis in FCR, while seven combinations had negative heterosis; three were significantly different from zero. No significant differences in mortality between the pure strains and the hybrids were found.

ISSN:0906-4702    

DOI:10.1080/09064709609415864

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

During three years (experiments 1-3) short-term grazing experiments were performed to study late season herbage intake by dairy cows. Change-over designs were used during experiments 1 and 2 while a continuous design with a covariate period was used in experiment 3. The effect of fouling on intake at a herbage allowance of 30 kg dry matter (DM) per cow and day was studied by comparing herbage intake on clean, grass-dominated pastures (treatment CG), with herbage intake on fouled grass-dominated pastures (treatment FG), in experiments 1-3. In experiment 2, a third treatment was included, consisting of grazing a clean clover-grass ley (treatment CC). Pastures on treatment CG were cut and those on FG were grazed and then immediately topped at the same times throughout the grazing season until the start of the experiment. In experiment 2, the grazing area of treatment CC was the regrowth after an early season harvest. The herbage intake on treatment FG was 13.0, 13.8 and 14.2 kg organic matter (OM) per cow and day in experiments 1, 2 and 3, respectively, while corresponding intake values for treatment CG were 13.7, 15.5 and 14.8 kg (OM). In experiment 2, the herbage intake of cows on treatment CC was 15.1 kg OM. The increases in intake observed on clean pastures were statistically significant (p < 0.01) in experiments 1 and 2 but not in experiment 3. Herbage intake was approximately 5-10% higher when animals were offered clean pasture compared with fouled.

ISSN:0906-4702    

DOI:10.1080/09064709609415865

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The basis for using determined values of endogenous ileal protein and amino acid losses in the protein evaluation of pig feeds is reviewed. The amounts of endogenous protein and amino acids in ileal digesta may be determined by numerous methods. These include N-free diets, regression analysis, enzyme hydrolysed casein (EHC) coupled with ultra-filtration, modifying lysine to homoarginine, isotope dilution techniques and calculations based on the difference between thein vitroandin vivodigestibility of protein and amino acids.

ISSN:0906-4702    

DOI:10.1080/09064709609415866

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

There is a distinction between the terms apparent, true, real, and “net” ileal protein and amino acid digestibility. For low-protein feedstuff's, “apparent” values relate directly to the feedstuff and are accurate estimates of net digestibility. For diluted protein-rich feedstuffs, apparent values underestimate the net digestibility, which, however, can be obtained from apparent digestibility by mathematical extrapolation.

ISSN:0906-4702    

DOI:10.1080/09064709609415867

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A total of 2152 hens were fed one of two diets, with 25.0% wheat and 38.7% barley or 50.0% wheat and 13.7% barley. The hens were housed in battery cages with three hens per cage and in two aviary systems with tiered wire floors and litter-Lövsta with two tiers and Marielund with three tiers. Two hybrids were used: ISA Brown and Lohmann selected Leghorn.

ISSN:0906-4702    

DOI:10.1080/09064709609415868

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A study was performed to investigate the effect of environmental temperature (18°C or 28°C) and increasing levels of pea fibre in the diet on digestive tract, visceral organ size, digestibility and energy metabolism in rats. Thirty-six male Wistar rats, initial liveweight (LW) 77-79 g, were allocated to six groups and housed at either 18°C (three groups) or 28°C (three groups). Three wheat starch, fish meal and pea fibre-based diets were prepared to contain 100, 200 and 300 g pea fibre kg−1(68, 110 and 157 g dietary fibre kg−1DM) and 160 g protein (N × 6.25) kg−1. One group of rats at each temperature was fed one of the diets for four balance periods. Gas-exchange measurements were made and urine and faeces were quantitatively collected. Food to gain ratio was higher (P<.05) at 18°C than at 28°C and increased (P<.05) as the level of fibre was increased. The weight of the visceral organs from rats housed at 18°C was higher (P<.05) than at 28°C. The empty weight of the small intestine, caecum and colon increased (P<.05) as the level of pea fibre was increased. The digestibility of DM, protein and dietary fibre (DF) was lower (P<.05) at 18°C than at 28°C. As the level of pea fibre was increased, the digestibilities of nutrients and energy decreased (P<.05). However, the digestibility of DF increased (P<.05) as the level of pea fibre was increased. The partial digested energy value for pea fibre was 11.9 kJ g−1. The metabolizable energy (ME) intake and heat production at 18°C (1128 and 974 kJ (W0.75day)−1respectively) were higher (P<.05) than at 28°C (831 and 674 kJ (W0.75day)−1respectively). As the level of pea fibre was increased, ME intake (W0.75day)−1and heat production (W0.75day)−1decreased (P<.05). Heat production as a percentage of ME was higher (P<.05) at 18°C than at 28°C: 86.6% and 81.2%, respectively. Heat production as a percentage of ME was higher (P<.05) for rats fed the 100 g pea fibre kg−1diet than the 200 or 300 g pea fibre kg−1diet. In conclusion, environmental temperature as well as DF influenced digestive tract and visceral organ size, digestion and protein and energy metabolism.

ISSN:0906-4702    

DOI:10.1080/09064709609415869

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0906-4702    

DOI:10.1080/09064709609415862

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor