Hay rich in water-soluble carbohydrates increases performance of dairy cows, irrespective of starch degradability supplementation

Water-soluble carbohydrate (WSC)-rich forages can increase the voluntary dry matter intake (DMI) of dairy cows and diet digestibility, often resulting in higher dairy performance. Most studies have been conducted at pasture or with alfalfa hay and little is known on natural grasslands hay and on the interactions between forage WSC and concentrate starch degradability on dairy performance. We aimed testing the effect on dairy cow performance of botanically diversified grasslands hay (rich or poor in WSC) and its possible interactions with concentrate starch degradation rate (low or high). Four equivalent groups of 14 Holstein and Montbéliarde cows, were fed for 9 week 4.8 kg DM/day of concentrate, 3 kg DM/day of 2ndcut hay and a high (WSC+) or low (WSC-) WSC content1stcut hay (ad libitum). One group per 1stcut hay type received a barley meal based (D+) and the other group received a corn meal based (D-) concentrate. The WSC+ cows ingested more WSC (+551 g/day) and had a higher WSC/crude protein ratio (+0.24) than WSC- cows. The resulting higher OM total tract apparent digestibility (+2.1%) of ingested diet improved milk (+1.4 kg/day) and fat (+58 g/day) yields and feed conversion efficiency (+0.05 g milk/kg DMI) of WSC+ compared to WSC- cows. The WSC+ hay diet induced lower milk urea (-91 mg/kg) and higher milk protein content (+1.1 g/kg) and yield (+59 g/day) compared to WSC-. The effect of concentrate starch degradation rate on dairy performance was not significant for either the WSC+ or WSC- diet.