Roughage Feeding of Suckler Cows during Winter. Intake, Utilization and Energy Status in Pregnant Cows

Beef cow and calf (suckler-based beef) production is based primarily on different types of grasses, which are fed as grazed and conserved forage. In Sweden, suckler cows are commonly wintered indoors and fed conserved forage during this period. As the cost of harvested grass usually is greater than that of grazing, winter feed costs constitute a substantial proportion of the total annual costs of feeding the cow.

A majority of the Swedish suckler calves are born in the spring. Consequently, the nutrient requirements of the spring-calving suckler cow are relatively low during a large part of the indoor period, as the cow does not produce any milk. Suckler cows are commonly fed forage ad libitum, i.e., in free access, during the winter for rational reasons. However, the combination of low nutritional requirements during early to mid-pregnancy and ad libitum feeding may result in an overfeeding with energy and protein during this period.

To regulate feed intake of pregnant suckler cows during ad libitum feeding regimes, a common strategy is to delay the harvest of grass. This results in forages with high concentrations of neutral detergent fibre (NDF) and low digestibility, which limits intake by providing high rumen fill. However, field studies have shown that traditional grass mixtures might have too high nutritive value for this animal category also when cut late. Over-conditioning of suckler cows during pregnancy is expensive and increases the risk of dystocia. On the other hand, negative energy status prepartum and poor body condition at parturition may have negative effects on cow reproductive performance and on calf weight gain and weaning weight. Overfeeding with protein may result in unnecessary losses of nitrogen, as protein supplied in excess of rumen microbial and cow requirements are excreted in urine. Thus, from economic, environmental and cow performance perspective, there is a lot to be gained by house holding with feed resources by feeding the correct quality and quantity at the right time.

The early maturing beef breed Hereford and the late maturing beef breed Charolais are two of the most common beef breeds in Sweden. They were historically developed on low and high quality forage diets, respectively. Today, Swedish breeding goals still dictate that Hereford should be bred for more nutritionally extensive production than Charolais. Hence, the question has been raised if intake and feed utilization in these breeds may. Such information is warranted as it could indicate if feeding recommendations should differ between breeds.

The aim of this thesis was to evaluate the nutritional quality of alternative types of high-fibre roughages, in addition to traditional grasses, when fed ad libitum to pregnant suckler cows. Our focus was to study the dietary effects on feed intake, utilization, nitrogen excretion, cow energy status before and around parturition, and calf performance, in an attempt to improve the effectiveness of feed resource use to spring-calving suckler cows.

Three feed trials were conducted at SLU Götala Beef and Lamb Research Centre, located in south-western Sweden. In the first trial, we studied the effects of feeding three late cut forage diets; timothy-, reed canarygrass-, and whole-crop oat silage, on intake, digestibility, rumination time, faecal particle size and nitrogen utilization in mid-pregnant cows of Hereford and Charolais breeds. In two further trials, four roughage diets; timothy-meadow fescue silage, festulolium silage plus urea, reed canarygrass silage, and barley straw supplemented with urea and rapeseed meal, were fed during the last 16 weeks of pregnancy to cows of the Hereford breed. Daily feed intake and cow changes in body condition, body weight and metabolic profile before and around parturition were measured continuously, whereas the dietary effects on nitrogen utilization were evaluated in mid-pregnancy. In the third trial, calf birth weight, growth and weaning weight were also recorded.

The results showed that although all perennial grasses were cut at similar stage of maturity, i.e. flowering, they exhibited differences in digestibility and fibre characteristics that were large enough to elicit differences in cow intake. Cows consumed greater amounts of the diets based on the more digestible timothy-, timothy-meadow fescue-, and festulolium silages, than of the other diets. Cows were able to consume nearly 1% of their body weight as roughage NDF, which could be used as a rough rule of thumb on farm level to predict feed consumption, provided the body weight of the cow is known and that a proper feed analysis has been conducted.

It was clear that the late cut traditional timothy-meadow fescue silage, and festulolium silage, became too nutritious for pregnant suckler cows, as they resulted in increased body weight and body condition prior to calving. Contrary, the low digestibility of the reed canarygrass and barley straw diets limited the cows' ability to increase intake to meet the demand of nutrients by the growing foetus during late pregnancy, which resulted in losses of body weight and body condition, and in an apparent energy deficiency in cows fed the barley straw diet. However, cow reproductive performance during the subsequent grazing period and calf performance did not appear to be affected by the nutritional level of the cow before parturition.

Utilization of dietary nitrogen was improved with increased intake of digestible organic matter, resulting in lower excretion of nitrogen in urine. Feeding silage of reed canarygrass resulted in the greatest urinary output of nitrogen, which probably was a result of its poor digestibility in combination with its relatively high concentration of protein.

Cows of the Charolais breed had greater daily dry matter intake than cows of the Hereford breed, but this difference was not significant when intake was related to cow body weight. Hence, intake appeared to be more related to the size of the cow than to the breed per se. We observed no differences in diet digestibility between the two breeds, even though differences in rumination time and faecal particle size existed.

The studies in this thesis indicated that there is potential to increase the effectiveness of today's traditional Swedish winter feeding of pregnant suckler cows. Feeding of roughages with high fibre concentrations and low digestibility can result in decreased intake and accompanied feed costs, as well as decreased risks for overfeeding of energy and protein, without negative effects on cow performance. To achieve the desired forage characteristics, the traditional grass silages of timothy and meadow fescue should be cut at a late stage of development, which might be even later than flowering. Late cut reed canarygrass might be a better alternative to traditional grasses, as it resulted in moderate reductions of cow body weight and body condition in late pregnancy and a lower feed consumption accompanied by a lower feed cost.