The long-term health and wellbeing of cows within a seasonal calving system is highly dependent on their fertility.
According to LIC, the national not-in-calf rate for spring calving herds averaged about 14 percent in 2012 (when mating was on average
85 days) rising to 17 percent in 2015 (when inductions were fully phased out) and 2016 and 2017 (when mating was on average 76 days). Approximately two thirds of the increase in cows not-in-calf can be explained by the shorter mating period; it has been estimated that 6-week in-calf rates would have to increase by about 4 percent to compensate for the shorter mating period.
The pressure is on to get a higher percentage of cows in-calf quickly. Many factors may affect fertility including the accuracy of oestrous detection, semen quality, the timing of AB and technique but nutrition is a key factor. The pre-mating period is a critical time to review the average
and spread of body condition score of cows and also assess milk quality and quantity, the mineral status of the herd (by diet analysis and blood tests if necessary) and identify non-cycling cows that need help.
Dairy cows with a predisposition to produce milk will peak higher if fed well post-calving and are vulnerable to extra stresses or challenges over mating. There is a risk to feeding grain for 5 or 6 weeks after calving to help fill a feed pinch and then stopping before mating. While many people feel pressured to reduce supplementary feeding as grass growth increases, this could cause cows to plunge into a negative energy balance.
If cows have had milk fever or mastitis, are skinny, late calving or just young or old cows struggling to gain condition prior to and through mating, their energy balance could be improved by milking them once per day (taking less milk, giving them longer to graze and less walking to the dairy shed) or by increasing the quality or quantity of supplementary feeding (to improve energy supply).
If milk yield, protein production or milk urea levels are dropping away quickly as mating approaches it is worth paying extra attention to pasture quality and if necessary, increase supplementary feed levels. If cows are slipping into a negative energy balance through mating, feeding more supplements or increasing the nutrient density of the supplements is worth considering. Rumen-protected fats are a safe option for increasing energy intake.
Some essential trace minerals have a key part to play in fertility. I wish there was a silver bullet that could be added to feeds which would greatly improve fertility but apart from correcting a deficiency in a diet I have not seen anything which significantly affects fertility when provided in a special form or luxurious amount. Indeed, I think farmers should be cautious of oversupplying trace minerals like iodine and selenium at rates many times above the National Research Council recommendations.
Resilience comes from an ability to adapt and respond – understanding what has impacted fertility previously and taking stock of how this season is going now could be worthwhile.
For further information, contact your local Nutrition Specialist.
Article supplied by Dr. Rob Derrick, NRM Lead Nutritionist.