Fertility remains among the major issues in dairy herds.

13 March 2009

Fertility remains among the major issues in dairy herds. Conception rates to first service continue to decline and currently average around 40%. In fact, more than a quarter of producers responding to a survey carried out by Volac earlier this season said fertility was a real issue within their herd. Volac’s Dr Richard Kirkland discusses why energy is a key factor influencing cow fertility and how it is proving to reduce calving index (CI) in official trials and on commercial units.

It’s quite simple; high yielding dairy cows suffer a period of negative energy balance in early lactation when their energy requirement to support milk production is greater than their energy intake from the diet due to low feed intakes in the weeks after calving. Consequently, they mobilise body fat to make up the shortfall in energy supply – clearly visible as cows losing body condition through the early lactation period.

Excessive body condition loss can lead to major health problems such as ketosis and fatty liver; however it is also directly correlated with reduced fertility. Recent work from the US showed that cows losing less than 0.5 units of body condition score (BCS) over the first 30 days after calving began ovulating by 28 days post partum. Cows losing 0.5 to 1.0 BCS took 38 days and, with excessive BCS loss - more than 1.0 unit over the first 30 days, cows didn’t begin ovulating until 44 days after calving. Furthermore, increasing negative energy balance not only delays ovulation, but reductions in conception rate of up to 10% per 0.5 unit BCS loss have been reported.

Like many issues with dairy cows, the effect of energy balance on fertility is closely linked to the hormonal balance of the animal and this has been evaluated recently in studies at the University of Nottingham. Cows losing excessive body condition in early lactation have low levels of the metabolic hormones, including insulin, which can lead to impaired ovulation. In practical terms, insulin production can be stimulated by feeding additional starch in the diet, but unfortunately this may reduce egg quality.

On the other hand, increasing levels of fat of particular fatty acid profile in the diet has resulted in improved egg quality. Fat also increases production of progesterone, known as the hormone of pregnancy, the level of which increases after ovulation and is essential to nourish and maintain the developing embryo. Dietary fat levels can be increased by supplementing diets with appropriate protected fat sources and offer an effective method of increasing diet energy density, ensuring more energy per bite, as fats contain around 2.5 times the ME concentration of cereals.

Clearly fertility is a complex subject and in reality it is difficult to feed individual cows for optimal hormonal balance however tight the calving pattern is. So, like many things in life, it’s about best compromise. Paying attention to achieving the ideal condition score at calving, 2.5 to 3.0, followed by feeding high energy diets to minimise negative energy balance will pay dividends in fertility improvements.  

Feeding an energy-enhanced diet supplemented with Megalac protected fat in early lactation increased fertility in a recent study with the University of Edinburgh’s Langhill herd. The 9,500 litre herd’s 100-day in-calf rate improved by 23.6 %, while calving to conception interval showed a numerical reduction of 19 days.

Commercial producers are also finding that similar energy-rich diets containing Megalac protected fat fed during early lactation are helping them to meet their herd’s target CI. Take David Talbot who manages a 180 cow pedigree Holstein herd calving all year round at Lower Alston Farm, Ribchester, Preston, currently yielding an average 9,300 litres. “We’ve adopted a high input, high output strategy and as the herd’s genetics are continually improving, we keep pushing for that bit more milk.

“We feed a high energy parlour concentrate supplied by Dugdale nutrition containing Megalac, supplying 13.6 MJ per kg, however last year we opened up a clamp of silage that was so low in energy we realised it needed additional supplementing, so we introduced a further 0.33kg Megalac per cow per day to the semi-TMR, supplying an additional 11.2MJ per kg.

“Apart from seeing an immediate yield increase, up an average two litres per cow per day, introducing more rumen protected fat to the high yielding cows’ diet has certainly helped to improve fertility. During the last 180 days, the average number of days to first service has fallen from 78 to 62 days, the average number of straws per conception has reduced from 2.2 to 1.62, and calving index has fallen from 420 days to 389 days. Furthermore, the cows have never looked so well; and they are calving at body condition score 3. Also during this period a heat mionitoring system was added.”

He adds: “Feeding a high energy diet is now part of the big jigsaw. We’ve just started three times a day milking and are targeting a 10,000 litre average; we are fully aware we have to continually appraise the herd’s management and nutrition and ensure we achieve that very fine balance if we’re to fully exploit its potential.”

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