Turn-out can mean turn-off, or at least cutting back on supplementary feed, however spring is a key period when energy levels should be maintained in the diet, says Volac nutritionist, Richard Kirkland.
Early spring grass is a nutritious feed but can only supply a limited proportion of the cow’s energy requirement. Cutting back sharply on supplementary feed will encourage the cow to “milk off her back”, lose body condition and consequently suffer fertility problems, which pose an underlying, yet real, cost to a herd.
The benefits of feeding energy supplements at turn-out were proven in a study undertaken within the commercial dairy herd at the University of Lancashire’s Myerscough College. Freshly-calved cows were offered a TMR ad lib, along with a parlour concentrate containing Megalac rumen-protected fat as an energy source at either 2% or 6% inclusion rates. The study continued for 16 weeks, with cows given access to grass at 12 weeks.
Cows fed the higher-energy diet produced a significant 2.3 litres more milk from calving to eight weeks, and maintained this over the 16-week feeding period. Allowing for the additional cost of the fat supplement, this represents a return of 26.2p a cow a day, or more than £4400 a month for a 150-cow herd on milk sales alone. Furthermore, milk composition was maintained during the trial period, despite the higher milk yield.
An added spin-off was the benefit to body condition score, a key factor influencing fertility. Cows had similar condition scores initially, but those offered the higher-energy diet maintained condition following turn-out, while those offered the lower energy diet lost condition, despite also producing considerably less milk.
Loss of body condition due to insufficient energy intake plays havoc with the cow’s hormonal system and can lead to ovulation of poor quality eggs. Research has demonstrated excessive loss of body condition after calving delays the cow’s return to oestrous, with Nottingham University reporting a reduction in conception rates of close to 5% for every 0.5 unit loss in condition score during early lactation. With conception rates to first service having fallen below 40% nationally, there is a clear need to be proactive in addressing herd fertility issues.
Data from the Agri-Food and Biosciences Institute, Hillsborough, has demonstrated that under optimal conditions cows can produce over 25 litres from grazing. However, performance achieved from grazed grass can be highly variable, influenced by factors such as weather conditions, grass quality and how much grass is actually available. Hillsborough data recorded over the past three years has shown variation in grass growth rate between 66kg and 113kg DM/ha/day during early to mid-May, highlighting the essential role of energy supplements to make up the shortfall in requirements, particularly where grass growth is poor.
Spring grass contains high proportions of rapidly-fermented sugars and rumen-degraded protein, while fibre content increases and sugar content decreases as the season progresses. As well as providing energy, supplements can be formulated to help achieve particular production goals. Previous studies at Hillsborough demonstrated an improvement in milk fat of almost 0.6% when high genetic-merit cows were offered a high-fibre – compared to high-starch – concentrate from early to mid-season, while milk protein was 0.16% greater with the high-starch supplement.
Results from the Myerscough herd add a further dimension to supplementation strategies at grass, demonstrating the particular role of protected fat during the grazing season. Young leafy pasture is highly fermentable, but supplemented fats increase energy supply without adding to the acid load in the rumen. Additionally, particular fats improve egg quality and increase production of the major pregnancy hormone, progesterone.
At a time when dairy margins continue to be slim, feeding an energy-rich diet this spring is an investment which will certainly pay dividends now and for the medium to long term. The Myerscough trial results confirm the benefits of high-energy, rumen-protected fat, not only during the winter housing period, but through the grazing season as well.