In terms of reproductive performance, if conservative by nature or restrained by budgets it might be worth starting with the little things and working up the food chain rather than concluding the big cost items are beyond reach and do nothing.
Essential trace minerals are reactive elements that are required in tiny amounts that get involved in many enzyme and hormonal systems throughout the body. Their effects are often quite subtle and deficiencies hard to detect because they can be associated with symptoms that could be related to a host of other things. As indicated in Table 1 some are particularly associated with reproduction so it could be prudent to check the herd’s status or supplementation levels in the critical pre-mating period. I would include the major minerals phosphorus and sodium to a mineral review at this time – especially when heifers have been wintered on fodder beet and fed maize silage in early lactation. Lameness and poor udder health could impact on a cow’s inclination to express oestrous so zinc methionine could be considered as a nutritional remedy to help in these areas.
It is widely accepted that reduced mating performance occurs if cows are underfed at mating time. Whilst a short period of underfeeding over mating may have little negative effects on reproduction for mature cows that are in good condition it is always difficult to know how long a period of underfeeding will last and thinner cows and heifers are more vulnerable to a period of under nutrition. Mating of spring calving cows can coincide with grass getting into reproductive mode at the same time, resulting in rising fibre and falling metabolisable energy and protein levels. If compounded by poor weather and lower sugar levels, energy intake drops and cows that were comfortably holding their own can enter a negative energy balance and milk production falls off peak faster than it would normally. In this situation, feeding supplements to fill a feed deficit seems eminently sensible if only to maintain milk flow irrespective of what logic would suggest it will do for reproduction. Preferentially feeding younger and thinner cows to improve energy status and body condition should increase the potential for successful reproduction. If a grain-based supplement is already being fed the rate can be increased if needed, possibly including some rumen-friendly fat help to close a negative energy gap but even protein should be considered if the total protein content of the diet is sub-optimal.
Table 1 Fertility issues associated with essential minerals and trace elements.
|Trace mineral||Symptoms if deficient|
|Copper||Poor fertility – delayed or depressed oestrus, abortion, poor semen quality|
|Iodine||Abnormal oestrus (irregular or suppressed). Resorption of fetus (early embryonic death).|
|Manganese||Low fertility in adults|
|Selenium||Infertility affecting oestrus, ovulation, embryo fertilisation and development|
|Zinc||Poor testicular development|
|Phosphorus||Irregular oestrus, silent heat, delayed/low conception|
|Sodium||Reduced reproduction efficiency through poor fertility in males|
Trying to stem the global fall in dairy cow fertility is difficult partly because statistically it is a lot harder to prove that a treatment significantly affects fertility – either positively or negatively – compared to something like milk yield. Cows are either pregnant or not, they can’t be half pregnant, whereas milk yield can be continuously variable and many other variables can affect the fertility outcome which have nothing to do with the imposed treatment. Unfortunately huge budgets are required to deliver enough replication in fertility trials to ensure the results can be trusted so scientists may not provide the answers soon.
Dr Rob Derrick