Roughage Feeding of Suckler Cows during Winter : intake, utilization and energy status in pregnant cows

Feeding late cut forage is a common strategy to provide pregnant suckler cows with feed of suitable nutritional quality during ad libitum feeding regimes. Despite this method, commonly grown grasses may result in overfeeding with energy and protein in relation to cow nutrient demands. The aim of this thesis was to evaluate alternative types of highfibre roughages and their effects on feed intake, utilization, and cow energy status, to improve the effectiveness of feed resource use to spring-calving suckler cows. In a first study, the effects of forage diet; timothy silage, reed canarygrass silage, and whole-crop oat silage, on intake, digestibility, rumination time, faecal particle size and nitrogen (N) utilization were studied in mid-pregnant cows of Hereford and Charolais breeds. In two further studies, feed intake, N utilization, cow energy status and metabolic profile before and around parturition, and calf performance, were investigated in Hereford cows fed timothy-meadow fescue silage, festulolium silage, reed canarygrass silage or barley straw supplemented with rapeseed meal during pregnancy. Although cut at similar stage of maturity, all perennial grasses exhibited variations in digestibility and fibre characteristics, which elicited differences in intake and utilization. Traditional timothy and timothy-meadow fescue silage, and festulolium silage, resulted in overfeeding and increased body weight (BW) and body condition (BCS) during pregnancy, whereas the low digestibility of the reed canarygrass and barley straw diets resulted in a catabolic state and losses of BW and BCS prepartum. Intake appeared to be proportional to cow BW and not affected by the breed itself. Nitrogen utilization was improved with increased intake of digestible organic matter. There is potential to increase effectiveness of the current suckler cow feeding by choosing alternative forages of low digestibility and rich in fibre. This may reduce feed intake and accompanied feed costs, and risk of overfeeding with energy and protein, without negative effects on cow performance.