Nutritional Factors Affecting Reproductive Performance in Gippsland Dairy Herds

This article outlines some of the effects of feeding a diet that doesn’t meet these nutritional requirements and will give some management strategies to optimise nutrition for reproductive performance.

Nutrient imbalances have been shown to reduce the reproductive performance of dairy herds, but the interaction between nutrition and reproduction is complex. Often the best recommendation dairy herds on pasture-based production systems is to provide enough supplements to keep the herd in positive energy balance while meeting its needs for protein, fibre, minerals and vitamins.

Energy

Negative energy balance in early lactation is likely to be the most important nutritional factor affecting reproductive performance of dairy herds. Despite the trend on many Gippsland dairy farms to reintroduce genetics that favor higher reproductive performance, our pasture-based production systems usually don’t allow cows to consume enough dry matter in early lactation to meet the nutrient requirements for milk production. The result is the mobilization of body tissues and loss of body condition.

Cows in negative energy balance are less likely to show signs of heat and tend to have longer intervals to first ovulation and first estrus, lower first service conception rates and more days open. Generally, the greater the negative energy balance, the longer the interval to first ovulation. In particular, the return of normal estrus activity after calving depends on the extent of loss of body condition in the first 3 weeks of lactation. Energy deficiency should be considered a problem in herds where cows are not cycling normally by 30-40 days after calving.

Returning cows to positive energy balance as early as possible after calving will improve reproductive performance. In Gippsland this can usually be achieved by implementing a good transition cow management program, maintaining high average pasture residuals in early lactation and feeding sufficient amounts of cereal grain-based supplements and conserved forages to match any shortfall in metabolisable energy coming from pasture. Maintaining a healthy functioning rumen is particularly important in maintaining dry matter and metabolisable energy intake. This can be achieved through the provision of adequate amounts of neutral detergent fibre from hay or silage, the use of rumen buffers such as sodium bicarbonate and/or acid buff, and the use of rumen modifiers such as Tylan® or Eskalin®.

Protein

Excessive protein intake by dairy herds can result in reduced reproductive performance. Reproductive performance may be reduced where protein intake exceeds requirements by as little as 10-15%, particularly when cows are in negative energy balance. Typically, more services are required per conception resulting in longer calving intervals. The difference in conception rates are associated with changes in pH and chemical composition of fluid in the uterus, lower blood plasma progesterone concentrations and higher blood plasma and milk urea concentrations.

While excessive intakes of both rumen degradable and by-pass protein are associated with reduced reproductive performance the intake of rumen degradable protein appears to be the more important factor. In Gippsland, joining often coincides with periods where concentrations of protein in pasture are at their highest. It is usually not practical to reduce the amount of crude protein in pasture as this will compromise rate of pasture growth and ultimately the amount of high quality dry matter available for milk production. Under these circumstances, the amount and composition of the concentrates fed in the bale becomes important in balancing the protein from pasture.
The composition of the concentrate supplement should be designed to utilize the rumen degradable protein from pasture and more closely match the balance of protein to energy required by the cow. Ideally it will consist of balance of cereal grains and by-products that provide a range of starch fermentation rates and that are low in rumen degradable protein. It will also contain some sugars to help mop-up rumen ammonia as well as a source of bypass starch and fats to help balance the amount of protein relative to energy in the diet and promote healthy ovarian and uterine function. For this reason adding cane sugar, choc malt and maize to concentrates during joining can help improve reproductive performance and is often recommended by Irwin Stockfeeds Nutritionists.

Minerals

While dairy herds can often continue to milk well for periods when the diet is deficient in minerals these diets can be the cause of poor reproductive performance in the current and subsequent lactations. Calcium and phosphorus nutrition around the transition period is particularly important as the occurrence of milk fever is negatively associated with subsequent reproductive performance, particularly the interval to first ovulation. Lactating cows should always be provided with enough available calcium and phosphorus to meet their immediate requirements for production as this will minimize health problems and help to ensure longevity in the herd.

Supplementation of pasture-based dairy herds in Gippsland with a high yield ground limestone is essential during early lactation in order to meet requirements for calcium. Supplementation of herds with a source of phosphorus, typically dicalcium phosphate or DCP, is sometimes required to prevent phosphorus deficiency during early lactation. Supplementation of herds with a high yield ground limestone, small amounts of DCP and vitamin D across the whole lactation can help increase calcium absorption and bone remineralisation leading to lower rates of milk fever and improved reproductive performance in subsequent lactations.

Trace mineral deficiencies are also associated with poor reproductive performance. Selenium deficiency has been reported to cause retained placenta, increased incidence of embryonic-fetal loss, abortions, increased incidence of metritis, a higher level of general infection and the birth of dead or weak calves in some herds. Iodine deficiency leads to inadequate thyroid function and this has been associated with reduced ovarian activity and conception rates. Copper, manganese, and cobalt deficiencies have been associated with impaired ovarian function, silent estrus and abortions.

Determining the need for supplementation of dairy herds in Gippsland with a given trace mineral can be achieved through forage and blood tests. Forage testing undertaking by Irwin Stockfeeds Nutritionists and blood tests of cattle undertaken by veterinarians on Gippsland dairy farms has shown that individual farms can suffer trace mineral deficiencies, typically deficiencies of copper and/or cobalt and/or selenium. There are many options to correct trace mineral deficiencies on farms, but for simplicity and cost effectiveness we recommend feeding a vitamin and trace mineral premix, such as Irwin Mineral Premix, as part of the supplement fed in the bale to the milking herd.

Summary

Poor reproductive performance in dairy herds is costly in terms of time and money. When nutritional problems are corrected, improvement in reproductive performance won’t become evident for some time. We recommend that you make use of the best available information on the nutrient requirements of your herd and run a feeding program which meets all known nutrient requirements. Irwin Stockfeeds Nutritionists make use of the most up to date recommendations for meeting the nutritional requirements of pasture-based dairy herds. We offer a feed and forage testing and interpretation service and can provide accurate estimates of nutrient intakes of your herd. Importantly, however, nutrition is only one possible cause of poor reproductive performance of herds and other possibilities and sources of advice should always be considered.

For nutritional advice speak to one of our qualified nutritionists:
Peter Lowry – East Gippsland 0409 566 543
Kristy Evans – West Gippsland 0417 500 344
Jake Frecklington – South Gippsland 0409 566 078