Winter diets – achieving the correct balance

6 November 2008

With the on-going quest for greater economies of scale and a substantial shortfall in British milk production this year, it’s hardly surprising that more than 50% of dairy farmers responding to a survey conducted by Volac at the recent Dairy Event and Livestock Show indicated they planned to increase milk yield this winter. Some 17% of producers said they aimed to increase milk fat % while 10% were targeting increased milk protein %.

These farmers were also more than aware of the consequences of pushing solely for yield; 39% indicated that lameness was an issue in their herd, while fertility and mastitis were also highlighted as major challenges.

Volac’s ruminant nutritionist, Dr Richard Kirkland, offers a six-point holistic approach to formulating balanced winter diets that will help exploit performance without detriment to herd health. Like most things in life, he says, it’s a case of achieving a balance meeting the cows’ needs with the appropriate level and type of inputs. 

1, Forage quality

Have you had your grass and maize silages analysed? With forage making up 50% or more of diets on most farms it is essential that you know its nutritional quality in order to formulate a properly balanced ration. This year’s grass silage analyses show major variations in quality across farms, so the potential of particular silages to contribute to cows’ energy and nutrient requirements may differ dramatically. Assuming an intake of 10 kg of silage dry matter (DM), a difference in metabolisable energy (ME) concentration of 1 MJ/kg DM, for example silage with ME of 10 compared to 11 MJ/kg DM, would result in 10 MJ less ME intake from the poorer quality silage, broadly equivalent to two litres of milk.

2, Yield

High yielding dairy cows suffer a period of negative energy balance in early lactation. Energy intakes can be maximised by increasing the diet’s energy density; this ensures that even where DM intake is limiting, the cow consumes more energy in every bite. Supplementing with cereals will increase milk yield and energy density, but inclusion should be limited due to potential build up of acid produced during rumen fermentation leading to acidosis. Alternatively, introduce protected fats; for example adding 0.5 kg of Megalac protected fat to a ration will typically lift energy density by 0.5 MJ/kg DM, but crucially will not add to the acid load in the rumen. Results from 18 studies collated by Penn State University researchers demonstrated that adding Megalac to diets improved yields by an average of 2.3 litres/cow/day, currently worth up to £1,100 additional profit from 100 milking cows per month. 

3, Milk fat

Milk fat % is strongly influenced by the starch/fibre balance of the ration. Supplementing rations with excessive amounts of highly fermentable starchy feeds acts to reduce milk fat, while fibre sources are the primary suppliers of the acetic and butyric acid building blocks required for milk fat production. Rations should have a minimum of 28% to 30% neutral detergent fibre (NDF) in early lactation and fibrous forages will provide a source of structural, effective fibre - rumen scratch factor - needed for good rumen function and buffering, to encourage fibre digestion and milk fat production. Feeding supplements with high levels of ‘free’ unprotected oil will reduce fibre digestion and can contribute directly to reduced milk fat synthesis by stimulating production of trans fatty acids in the rumen.

4, Milk protein

Starchy feeds stimulate milk protein and promote growth of rumen micro organisms which then contribute to the overall protein supply. Bypass sources of protein are needed to balance the cow’s total protein requirements and to supply essential amino acids - the building blocks of protein. Milk protein has a specific amino acid profile which must be met, and methionine and lysine are usually considered the two first-limiting amino acids for dairy cows. Soyabean meal and prairie meal are reasonable or good sources of bypass protein and supply high levels of lysine and methionine, respectively.

5, Fertility

Increasing energy balance - improved body condition score - has a major impact on fertility; cows losing body condition have a longer interval to first service and poorer pregnancy rates.

Insulin, a hormone fuelled by starchy feeds, stimulates follicle cell development and ovulation, while some fat supplements are proven to increase follicle size prior to ovulation, improve egg quality and increase production of progesterone, the ‘hormone of pregnancy’. These effects lead to a greater chance of fertilisation and sustained pregnancy.

6, Lameness

Ruminal acidosis is widely known as a causative factor of lameness. This again emphasises the need for a balanced approach to rationing to provide those essential carbohydrates needed for production while avoiding over-consumption of rapidly fermentable sources without adequate buffering. 

Clearly it is important to carefully consider the ingredients that will provide a balanced supply of energy, protein, fibre and fat in the ration this winter if targets for both productivity and health parameters are to be met, cost-effectively.

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