Choice of grazed herbage or maize silage by lactating dairy cows: influence of sward height and concentrate level / Preferência por pastagem ou silagem de milho por vacas leiteiras em lactação: influência da altura do pasto e do nível de concentrado

The preference of lactating dairy cows for grazed herbage or maize silage (MS), simultaneously offered ad libitum in the field, was examined at two sward heights (SH 4-6 and 8-10cm) and two concentrate levels (CL 0 and 6kg day-1) in a 2x2 factorial arrangement within a completely randomised experimental design. The experiment lasted 35 days and was carried out in spring using 24 multiparous Holstein Friesian cows. On average, the cows proportionately spent more time grazing than eating MS (0.85:0.15) and even though the higher rate of intake (RI) of dry matter (DM) of MS compared with grazed herbage (76 versus 26g DM min-1), the proportion of total DM intake as herbage was higher compared to that of MS (0.56:0.44). The higher crude protein and low fibre content of grazed herbage appeared to have a higher priority of choice than RI, as the cows chose to graze for longer (grazing time 385 min, MS feeding time 67min) despite the lower RI of herbage. The low proportion MS intake indicated that RI was a secondary factor of choice. Concentrate supplementation had a greater depressing effect on herbage intake than on MS intake. These results suggest that the animals reduce the intake of feed with lower RI when the labor associated to eat is decreased. The factors influencing the choice for herbage over maize silage remain unclear.

A preferência de vacas leiteiras em lactação por pasto ou silagem de milho (SM) oferecidas ad libitum simultaneamente no pasto foi avaliada quanto a duas alturas de pastagem (4-6 e 8-10cm) e dois níveis de concentrado (0 e 6kg dia-1), em um arranjo fatorial 2x2 dentro de um delineamento inteiramente ao acaso. O experimento, com duração de 35 dias, foi executado na primavera utilizando 24 vacas multíparas da raça Holandesa. As vacas passaram, em média, proporcionalmente mais tempo pastando do que comendo SM (0,85:0,15) e, mesmo considerando a maior taxa de consumo (TC) de matéria seca (MS) de SM comparada com a da pastagem (76 versus 26g MS min-1), a proporção do total do consumo de MS como pastagem foi mais alta comparada com aquela da SM (0,56:0,44). A proteína crua mais alta e o menor conteúdo de fibra da pastagem pareceram ter prioridade na escolha pelos animais do que a TC, pois as vacas preferiram pastar por mais tempo (tempo de pastejo = 385min, tempo para comer SM = 67min), não obstante ter havido menor TC na pastagem. A baixa proporção de consumo de SM indicou que a TC foi um fator secundário na preferência dos animais. A suplementação concentrada teve maior efeito depressor no consumo de pastagem que o consumo de SM. Estes resultados sugerem que a prioridade dos animais, quando o trabalho associado com o comer é reduzido, é o de diminuir o consumo de alimento com menor TC. Os fatores que influenciaram a preferência por pastagem sobre silagem de milho ainda não são totalmente claros.

Influence of genetic merit and environment on somatic cell counts of Holstein-Friesian cows.

Financially, mastitis is one of the most important diseases affecting dairy cattle in the United Kingdom. Seven commercial farms were monitored over a 2.5 year period and data from 1040 cows were included in a study that examined both straw yard and cubicle housing systems. The influence of genetic merit for milk production (PIN(95) and PTA(f+p)) on somatic cell counts (SCC) as an indicator of mastitis under commercial farm conditions was assessed. The mean genetic potential ( poundPIN(95)) was 39.0 (+/-0.80) and the mean 305-day milk yield (kg) was 7980 (+/-54.2). In all, 5618 monthly records of SCC and 1040 records of 305-day SCC were included in the analysis. A multiple regression model was used to assess the influence of genetic merit and the level of concentrate intake on SCC (the log(10) transformation was used) under the two housing systems. Significant interactions between genetic merit and housing system, and concentrate intake and housing system were found. Log(10) SCC increased with genetic merit when cows were housed in straw yard accommodation, but decreased when cows were housed in cubicle accommodation. The increase in SCC with concentrate feeding was higher for straw yards. For parity 2 animals, there was a significant positive correlation between PIN(95) and SCC (r(p)=0.184, P=0.003) but the correlations between 305-day milk production and SCC were negative for animals greater than parity 2.

Possible roles for prolactin, thyroxine and insulin in the growth of heifers before and during early pregnancy.

Two groups of British Friesian heifers with cyclic ovarian function and the potential for further growth were individually fed a restricted diet at two levels over a 12-week period. Eight heifers receiving the higher level of feed (SP group) and five receiving the lower level (LP group) became pregnant by artificial insemination at week 6. Mean (and SEM) body weight changes in the SP and LP groups were respectively 0.24 (+/- 0.024) kg day-1 and -0.19 (+/- 0.039) kg day-1. Over the period from weeks 3-12, mean concentrations of plasma prolactin, thyroxine and insulin in the five LP heifers were 39%, 67% and 74%, respectively, of those in the eight SP heifers. The results suggest that prolactin, thyroxine and insulin have roles in the growth of heifers before and during early pregnancy.

Corynebacterium pyogenes mastitis among heifer calves.

In August 1975 an outbreak of C pyogenes mastitis occurred involving 18 heifer calves at the National Institute for Research in Dairying. This paper describes the outbreak which affected animals varying in age from five to 22 months. Fourteen of the cases (77%) were among calves less than 10 months old. The advisability of using fly control measures among young stock in the summer months is discussed.