By Dr Kelly Plozza B.VetBiol/BVSc (Hons 1)
Body Condition and Effects on Conception and Overall Fertility.
As part of her current Masters project, our Melbourne University Resident, Dr Kelly Plozza has looked at the reproductive performance of cows in different body condition scores. This is part of a larger project looking at alternative treatments to improve the reproductive performance of non-cycling cows. This article will be part of a series looking at the effects of body condition on reproductive performance.
The likelihood of a cow conceiving to an insemination (whether that be with artificial insemination or a bull) is dependent on a variety of factors, with some of the main areas that are often focused on being insemination technique, and semen storage and handling (thawing technique). Other factors which are less often focused on as being contributors to poor conception are cow factors such as body condition and days in milk.
Cow Factors; How do they affect conception rate?
In order for a cow to maintain a 365 day inter-calving interval (seasonal calving pattern) she needs to conceive within 85 days of calving. This is quite a big ask when we think about it, as it takes quite a concerted effort for a cow to go through calving successfully, remain healthy in the post-calving phase, restore her uterus to a pre-pregnant state, tolerate the demands of lactation, restore her metabolism to a positive energy balance and also begin cycling! Therefore identifying factors which may assist with monitoring of these physiological changes is useful in determining how likely a cow is to conceive once she is inseminated. It is highly recommended therefore that body condition as well as other health parameters be monitored regularly as these are considered to be very important risk factors in regard to a cow’s likelihood of conceiving when inseminated.
As I have mentioned in earlier articles, Body Condition Score (BCS) in Australia is measured on a 1-8 scale and is used as a means of assessing the nutritional status, or energy balance, of an individual cow. It can also be used across a herd, to establish the overall nutritional and energy status of the cows. It is very useful information to know what the average BCS of your herd is, as this allows you to identify areas for improvement, if needed.
Cows inevitably lose body condition post calving to enable them to meet the demands of lactation through mobilization of body fat for energy. Unfortunately because of the modern cow’s priority towards high milk production, it is often impossible to prevent some body condition loss in the early period post-calving. However the amount they lose is very important, and on average for a herd, this should be no more than 0.6 of a body condition score in the period between calving and mating, and this may indicate inadequate nutrition in early lactation. Because of this obligatory loss, it is also very important to ensure that cows are dried-off and calve in adequate body condition to allow for this loss in the early lactation period. See below for recommendations;
As part of the research project being completed currently assessing over 3000 cows, it was found that there was an 18% difference in first service conception rate (FSCR) between cows that were in body condition <4 and those that were in body condition score greater than 4.5 at the point of mating and a 32% difference in 6 week In-Calf rate. This is a very important finding and highlights the extreme importance of ensuring adequate body condition, not only at the start of mating, but at dry-off and at calving.
Other Risk Factors
As mentioned earlier, the time since calving or days in milk (DIM) also impacts the likelihood of a conceiving to insemination, as understandably, it takes time for the uterus to return to a normal size and function after calving and become a healthy hospitable environment for egg fertilisation to occur with the introduced sperm. It has also been shown that being in a negative energy balance negatively affects the quality of the egg that is ovulated, so the longer a cows has been calved, the more likely she is to be in a positive energy balance and be capable of producing a healthy egg for fertilisation.
Because of the importance of both body condition score as well as days in milk it was interesting to see what the overall difference was between low and high body condition and low and high DIM when the two risk factors were combined. As can be seen below, the overall difference in reproductive performance for cows calved <60 days and in BCS <4 (Group 1), and cows calved more than 90 days and in BCS 4.5 or greater (Group 9) was 35% in FSCR and 54% for 6-week in calf rate. This is a profound difference, and clearly demonstrates the importance of both body condition as well as days in milk in improving the likelihood of conception.
It is suggested by the InCalf research project that every 1% increase in 6-week In-Calf rate has a benefit of $400/100 cows/year, therefore by increasing the average body condition of your herd, this will result in economic returns through improved reproduction as well as increased production.
Other risk factors that shouldn’t be overlooked include age, as older cows are less likely to conceive than younger animals, and in this particular study younger animals had almost double the likelihood of conceiving to first insemination than animals over the age of 6 years.
And lastly, it is important to remember that the post-calving period is a fairly risky time for a dairy cow, and diseases such as milk fever, retained foetal membranes (RFMs), Metritis, Endometritis, Ketoacidosis, and Displaced Abomasums (LDA’s and RDA’s) are all likely to impact their ability to conceive. Therefore managing disease through this period is paramount. Overall, ensuring cows are in good health and body condition when they are dried off, maintaining them in good condition through the dry period, and combining this with an effective transition management program, is all essential for future reproductive performance and improve the likelihood of conception when the mating period commences.
For more information regarding the importance of body condition and the effects on reproductive performance, come along to one of our upcoming FARMCHATs, where more information on this important research will be available.