Effect of time of maize silage supplementation on herbage intake, milk production, and nitrogen excretion of grazing dairy cows.

Supplementation of concentrates or maize silage on pasture often results in substitution and therefore a reduction in pasture intake, which defeats the object of increasing dry matter (DM) and energy intake. The reason may be twofold, one is simply loading of the rumen and the other is fermentation of starch from the grain depresses fermentation of the herbage in the rumen, thereby limiting its intake. Different methods have been employed to limit substitution, one is timing and period of supplementation. This was the topic of the study of Dr Al-Marashdeh and colleagues which they published in the Journal of Dairy Science, Volume 99 of 2016, pages 7132-7132, the title being: Effect of time of maize silage supplementation on herbage intake, milk production, and nitrogen excretion of grazing dairy cows.                       

The objective of their study was to evaluate the effect of feeding maize silage at different times before a relative short, intensive grazing period, on DM intake, milk production and nitrogen (N) excretion of dairy cows. Thirty-six Friesian × Jersey crossbred lactating dairy cows were blocked in nine groups of four cows by milk solids, production, body weight, body condition score and days in milk. The groups were then randomly assigned to one of three replicates of three treatments: (1) control, herbage only; (2) supplemented with 3 kg of DM per cow of maize silage after morning milking approximately 9 hours before pasture allocation (9BH); and (3), supplemented with 3 kg of DM per cow of maize silage before afternoon milking approximately 2 hours before pasture allocation (2BH). Above ground level herbage allowance was 22 kg of DM per cow per day for all groups of cows. Cows were allocated to pasture from 15:30 to 20:30.

Maize silage DM intake did not differ between treatments, averaging 3 kg of DM per cow per day. Herbage DM intake was greater for control than 2BH and 9BH, and greater for 9BH than 2BH (11.1, 10.1 and 10.9 kg of DM per cow per day for control, 2BH and 9BH, respectively). The substitution rate (kilograms of herbage DM per kilograms of maize silage DM) was greater for 2BH than for 9BH. The production of milk solids was similar between treatments (overall mean 1.2 kg per cow per day). Body weight loss tended to be less for supplemented than control cows (−0.95, −0.44 and −0.58 kg per cow per day for control, 2BH and 9BH, respectively). The estimated urinary N excretion tended to be greater for control than supplemented cows when urinary N excretion was estimated from plasma or milk urea N. During grazing, the non-esterified fatty acid concentration was greater for control than for supplemented cows and greater for 9BH than for 2BH (0.58, 0.14 and 0.26 mmol per Litre for control, 2BH and 9BH, respectively).

It is clear that timing of maize silage supplementation relative to a short and intensive grazing period can reduce the substitution rate and increase the herbage DM intake, but the results are not all positive.