Inter-breed relationship of maintenance efficiency to milk yield in cattle

Abstract

As part of a multibreed cattle project for studying genetic variation between breeds, four adult females from each of five breeds of cattle were kept for up to 2 years in a non-pregnant, non-lactating state on each of four feeding levels. The breeds, which were Hereford, Aberdeen Angus, Dexter, British Friesian and Jersey, provided a wide range of genetic potential for body size and milk yield. The feeding levels were arranged to make the weight of lipid in the whole body about 0·05, 0·15, 0·25 and 0·35 times body weight. After an animal had been assigned to a fixed daily intake, its body weight and condition score were monitored over a period varying from 6 to 18 months until an equilibrium body weight and body composition had been established.For standard adult body weight, Akg, and for an equilibrium body weight, Wkg, and an associated metabolizable energy intake, f/MJ, the maintenance efficiency of a breed adjusted for breed size was defined as Em = W/fA0·21. The ‘lactability’ of a breed, that is, its genetic potential lactation yield, Ykg, adjusted for breed size, was defined as Y = Y/A. The between-breed regression of Em on Y had a coefficient of -0·043 (s.e. 0·007). There was, thus, a highly significant dairy-beef gradient in the equilibrium maintenance efficiency of these non-pregnant, non-lactating adult females.An expected value for the equilibrium maintenance requirement, of a breed or individual as a function of its lactability was estimated to be:which implies that the maintenance requirement of dairy breeds is about 0·2 times greater than that of beef breeds, a result which was strongly supported by a literature survey, although mean estimates from feeding trials and fasting trials were anomalous.Combining this result for milk yield with published results on growth rate, leads to the hypothesis that the greater the maximum gross efficiency of a breed for meat or milk production, the less efficiently it maintains itself, not because of any difference in fasting metabolism, but because of a reduced efficiency of food utilization for maintenance.

Correlated responses in maternal performance following divergent selection for heat loss in mice1

“…In our case, mice selected for greater maintenance requirements have demonstrated greater milking ability and are the same size. Taylor et al (1986) compared maintenance requirements of low and high milking breeds of cattle. They found that beef breeds had lower maintenance requirements than those of dual-purpose breeds.…”

Strategies for defining traits when calculating economic values for livestock breeding: a review

“…For example, breeders may be interested in increasing the growth rate of progeny till weaning and during fattening. However, exclusive selection on increased growth rates will often result in higher mature weight as well (Taylor et al, 1986). As a consequence, selection of bulls for a high growth rate in a performance test has resulted in increased mature weight of dairy and beef cows in recent decades.…”

Uso do abate comparativo na determinação da exigência de energia de mantença de gado de corte pastejando capim-elefante: descrição da metodologia e dos resultados

“…Diferenças genéticas podem ocasionar mudanças de 20 a 30% nos requerimentos, sendo a característica moderada a altamente herdável (Taylor & Young, 1968). Entre diferentes raças, ocorrem correlações positivas do nível de exigência de energia de mantença com o potencial gené-tico de produção de leite e com a taxa de crescimento (Ferrell & Jenkins, 1985;Taylor et al,1986) Parte das diferenças nas exigências de mantença entre raças deve-se a variações nos tamanhos relativos dos tecidos ou órgãos do corpo. A atividade metabólica da proteína corporal é muito mais intensa que a do tecido adiposo, o que tende a elevar as exigências de energia de mantença, por unidade de tamanho metabólico, em animais com maiores proporções de músculos ou de menor maturidade fisiológica (Garrett,1980).…”