A worldwide drop in dairy cow fertility has spurred a New Zealand study.
Victoria University of Wellington researcher Janet Pitman wants to find out why some dairy cows are less fertile than others, and how to bridge the gap.
The reproductive biology expert from Victoria's School of Biological Sciences said part of the problem was dairy farmers selecting cows for high milk yields.
''This creates a population of cows that use much of their energy to produce milk, with the consequence that less energy is directed towards fertility,'' Dr Pitman said.
The amount of energy used to produce milk each day was equivalent to cycling a mountain stage in the Tour de France.
''What we are asking cows to do in a conventional New Zealand pastoral-based system is demanding, so it's not surprising that fertility suffers,'' she said.
Dr Pitman was in charge of the university's involvement in the seven-year research programme led by DairyNZ. The $40 million project was co-funded by DairyNZ and the Ministry of Business, Innovation and Employment, with core science funding from AgResearch.
Victoria University would recreate the natural fertility environment in a laboratory.
''We will then be able to immerse cow eggs in these artificial conditions and treat them with factors they might be exposed to during lactation, to see how well they cope,'' Dr Pitman said.
''Measuring the differences in the eggs exposed to the different environments will help provide indicators of infertility in dairy cows and may help design better diets.''
Previous research by the same Victoria University group in collaboration with University of Queensland, DairyNZ, University of Auckland, AgResearch and Cognosco showed that in early lactating dairy cows, about 21 to 42 days after calving, the follicular fluid surrounding the egg was much lower in amino acids than in non-lactating cows.
''We found that eggs exposed to very low amino acid environments were quite fragile and couldn't cope with the presence of additional stressors, such as non-esterified fatty acids and low cholesterol levels,'' Dr Pitman said.
She was now trying to find a way around that.
''We're thinking about what we can feed to dairy cows that may help increase the amino acid composition in the follicular fluid and allow the egg to better cope with other stressors.''