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Tasmanian Institute of Agriculture

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Published: 11 Apr 2019

Jersey cows

Samantha Flight, TIA

Conception rate is an important driver of in-calf rate. We all know that. But sometimes it easy to get side-tracked with the misconception there is a ‘silver bullet’ that will allow us to achieve high conception rates and hence high in-calf rates. As Charlotte Westwood, a nutritionist with PGG Wrightson Seeds, highlighted at the 2019 Tasmanian Dairy Conference, there is no escape from the reality that to consistently achieve high in-calf rates, we need to get the basics right.

Cow Body Condition Scoring

“Can’t manage what you don’t measure”

Cow condition score at calving has the greatest impact on the 6 week in-calf rates via improved submission and conception rates.

Your herd is likely to be underperforming if:

  • More than 15% of cows are calving in a body condition score less than 4.5
  • The 3-week submission rate is lower than 75% (greater than 86% should be achievable)
  • There is ovulation but no oestrus expression (silent heats)
  • Conception rate is lower than 49%

While we often the focus on the average condition score, Charlotte encouraged people to assess individual cow body condition score (BCS). There is always going to be a range of BCS within the herd. Even at an average condition score of 5, there are likely to be some cows that need attention because their individual score is too low or too high.

If condition score at calving is something that needs to be improved on your farm, a feed budget is a useful tool to help plan feed strategies through the late lactation and dry period. Often this is a matter of feeding extra dry matter during this period. Solutions to consider include:

  • Cool season active grasses that will increase the amount of dry matter grown during this period
  • Forage crops
  • Lower protein and higher energy feeds to help cows partition energy to weight gain (taking care not to over-fatten)

More information on BCS is available on the Dairy Australia website:  

https://www.dairyaustralia.com.au/farm/animal-management/fertility/body-condition-scoring.

Negative Energy Balance

Almost all cows experience negative energy balance (NEB) in early lactation This typically occurs after calving when a cow isn’t able to consume enough energy to meet her requirements. As a result, body condition decreases. In terms of reproductive performance, it is important this body condition loss isn’t too large (it should be less than 0.6 BCS) or too prolonged.

“Cows with good pre-calving appetite eat better POST-calving”

Encouraging the appetite of cows will help reduce the time they spend in the NEB hole. Focus on feeding through the transition period and start transition feeding 21 days pre-calving. Also pay attention to feed during the colostrum period – sometimes colostrum cows can be put in paddocks that are convenient but don’t have much feed, or because the number in the herd changes daily the allocation of feed might not be accurate. Charlotte emphasised the need to feed them well right from the start of their lactation by:

  • Allocating as much feed to the colostrum cows as they’ll eat (clean up residuals with milkers)
  • Providing the best quality forages on the farm
  • Stepping gradually through the changes from pre-calving to milker mobs
  • Continuing to address their metabolic needs (e.g. magnesium, calcium, phosphorus)

Charlotte encouraged people to consider once-a-day milking for the colostrum herd as it reduces energy demand and stress during this early part of the lactation. However careful monitoring for mastitis is needed particularly for cows with high genetic merit.

Quickly addressing any health conditions such as mastitis, ketosis, milk fever or infections is important not only because of individual cow welfare but because of the impact on appetite. Sick cows lose their appetite which results in greater body condition loss, milk production loss and lower conception rates.

Dietary protein and reproduction

Charlotte finished her talk by discussing the question of whether high protein diets have a negative impact on reproductive performance. High protein diets are sometimes blamed for delaying the onset of ovulation. However, there is not much evidence of this either from research or in practice. If high protein diets caused low conceptions rates it would mean good conception rates could not be achieved on high protein pasture diets and this is obviously not true as many Tasmanian and New Zealand pasture-based herds achieve excellent conception rates. This is because cows are able to adjust the rumen and liver to chronic exposure to high protein diets.