Seasonality of calving in pasture-based dairy systems: its effects on herbage production, utilisation and dry matter intake

Abstract

The objectives of the present work were to evaluate the influence of season of calving on (i) pasture productivity, (ii) total dry matter intake by cows, and (iii) the relationship between intake and milk yield of individual cows. Three systems in which the cows calved either in autumn, in spring or half in autumn, half in spring, were managed according to a set of common guidelines during 3 consecutive years. Herbage accumulation rate (HAR) was estimated by the difference between 2 successive grazings (pre- and post-grazing herbage mass). Average HAR in each month was similar between systems. However, small differences in HAR were observed between calving systems in spring and summer, and appeared to be related to the proportion of the farmlet closed for silage. Herbage dry matter intakes varied seasonally (P<0.05), but independently of the calving system (P>0.05). Cows from different calving systems, offered 8.9 or 2.5 kg maize silage dry matter per cow daily in the paddocks, consumed an average of 6.0 and 1.4 kg, respectively. A large variation in intake was observed between individual cows with ranges from 2 to 10 kg and 0.2 to 2.9 kg, respectively. In conclusion, applying the same grazing management decisions to systems with contrasting calving dates resulted in only small seasonal, but not annual, differences in pasture HAR. The results also indicated that when maize silage is fed in the paddock, wastage can be high and variation in intake between individual cows can also be large.