Random Variation in Voluntary Dry Matter Intake and the Effect of Day Length on Feed Intake Capacity in Growing Cattle

Photoperiodic effect on live-weight gain of bull calves

The effects of day length, of the daily change in day length and of heat load, together with age effect, on live-weight gain of Holstein-Friesian bull calves, were studied using 8205 gain records of 1019 calves that were maintained in the experimental herd at Newe Ya'ar during a 5-year period (1991 to 1995). The age range of the calves was 150 to 450 days. Effects of day length (h) and of day length change (min/day) were assumed to be linear and effect of age was assumed to be quadratic. Three heat load indexes were calculated, accounting for day temperatures above 27°C, or night temperatures above 18°C, or both, and their effect was assumed to be linear also. Random effect of calf and fixed effect of the year were also accounted for by the regression analysis. The mean gain was 1·274 kg/day. The effect of day length was 0·027 (s.e. 0·003) kg/day per h, and effect of day length change was 0·042 (s.e. 0·003) kg/ay per min/day both effects being highly significant (P < 0·0001). The effects of heat load according to each of the three indexes were either not significant, or tended to be positive, which implies increased gain with increasing heat load. Effect of age was positive (P = 0·0005), and of age2 was negative (P < 0·0001). Based on the regression model that did not include heat load effect, the peak gain was obtained on 19 May, 33 days before the longest day and the trough was obtained on 18 November, with a difference of 0·206 kg/day (proportionately 0·15 of the peak gain) between peak and trough gains. It was calculated by the regression coefficients for the photoperiod effects, that a calf that enters the feedlot at the age of 150 days and a live weight of 180 kg on 1 January, will be 23 kg heavier at the age of 350 days than a calf that enters the feedlot at the same age and weight on 1 July. This difference is reduced to 10 kg at the age of 450 days.

The influence of day length and temperature on food intake and growth rate of bulls given concentrate or grass silage ad libitum in two housing systems

In order to study the effect of day length and temperature on performance, data from 495 growing, non-castrated bulls of the Swedish Red and White breed were analysed. Groups of 11 bulls were housed in either an insulated building in pens having slatted floors or in an uninsulated building with pens having both a deep straw bed and a concrete floor. The majority of the bulls (330) were given a concentrate diet ad libitum, while the remainder (165) were given grass silage ad libitum supplemented with concentrate. Energy intake, live-weight gain, housing temperature, day length and change in day length were calculated as 14-day period means for the two housing systems. Regression analyses showed that live-weight gain was associated with increasing day length in bulls on both feeding treatments. For bulls given concentrate ad libitum, metabolizable energy intake was associated with increasing day length. The intake of heavier animals was more influenced by day length than that of those which were lighter. The seasonal influence on daily energy intake in bulls given silage did not show the same pattern as for bulls given concentrate ad libitum. The intake was highest in June and lowest in December for the bulls given concentrate but for the bulls given silage it was highest in August, September and October and lowest in March and April. This was due to the varying quality of the grass silage over the year. No effect or very little effect of temperature or housing system on energy intake or on weight gain was found.