#2 Breeding for fertility Good fertility is a combination of factors related to management and breeding. A low genetic level for fertility means you will need a high level of management to achieve good reproduction results. It is therefore important to consistently use bulls with a high genetic level of daughter fertility. Please note that a breeding focus on reproduction is something that does not show through in the herd until three to seven years later. It is a long-term solution. However, doing this will have a huge and gradual cumulative effect from generation to generation. Finding the problem The genetic level for fertility in the herd should not be below the breed average. If you have reproduction issues in your herd and the genetic level is below breed average, you should focus on selecting bulls with the aim of improving this when you plan your breeding strategy. Action plan Selecting the best AI Bulls based on the Nordic Total Merit Index (NTM) will improve the genetic level for financially important traits, including fertility. There is a strong positive correlation between NTM and daughter fertility (39% for Holstein). Make sure you use the best bulls for daughter fertility and avoid having too much focus on improving production alone, as these two traits have a strong negative correlation (-29% for Holstein). Crossbreeding is also a way to improve the reproduction results through breeding. Crossing with different breeds will give offspring with a better breed average than their parents, due to hybrid vigour. Focus areas • The herd’s breeding level for fertility • Use the best bulls for daughter fertility (with high NTM) • Avoid having too much focus on improving production alone • Crossbreeding as a solution #3 Barn conditions Optimal lighting conditions Multiple studies have shown that a day length of 16-18 hours and darkness of 6-8 hours have a positive influence on growth and age of sexual maturity in heifers, with no negative influence on the yield potential of the animals. Furthermore, this combination of lighting is thought to affect the dry days and the number of services in a positive way. Depending on which part of the world you live in, you may need to supplement the daylight with artificial lighting to reach the optimal length of day light. In this case, pay attention to the time shifting to night light – you may have to leave the light on for a few hours longer. Finding the problem Check if lighting system is sufficient. If in doubt, we suggest you buy a lux meter and measure the lighting yourself. Or contact your local cattle consultant or an electrician to do this measurement. The measurement should be taken one metre above floor level when comparing with the recommended level. Causes The positive effect is due to a signal being transmitted to the brain when light reaches the retina. This signal suppresses the production of melatonin. The rhythm in the production of melatonin is significant for a number of hormones that affect the growth, reproduction, milk yield and health of the animal. This means that the positive effect of lighting is only achieved when the animals go through a period of darkness during the course of a 24-hour period. Focus areas • Cows and heifers should have approx. 16 hours of light (>100 lux) • Cows and heifers should have approx. 8 hours of darkness (<10 lux) • Avoid concentrated pools of light during the hours of darkness. If the night lighting consists of leaving a few light sources in the barn on during the night, the lighting level will vary significantly in different parts of the barn. Areas of concentrated pools of light should be avoided in the barn as this will reduce the positive effects of the period of darkness. Action plan Lighting in a barn is best reflected from a light and clean environment – clean windows, skylights/windows, roof sheets and internal surfaces. 4
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