EBBE - How Nutrition Affects Bovine Ovulation
The topic of nutrition and how it relates to egg/ovarian health is very broad and involves many aspects.
22 July 2014
6 minute read
Background
The main areas of interest are ovarian health per se, uterine health and its cross talk with the embryo, disturbance of this mechanism through diseases such as metritis which play an important role in embryo loss. The oocyte is very vulnerable to metabolic insults which make conditions such as overweight cows (ketosis) and hypocalcemia particular risk factors.
To ensure optimal ovarian health primary focus should be placed on late lactation and the dry period. The drop in DMI intake around this period is considered to be one of the main problems and while the rate of fertilisation of oocytes is high the apparent low rates of pregnancy are due mainly to weak oocytes and embryos. Attempts to avoid stress around calving and first service a also a very important factor to consider around when trying to get a cow pregnant.
When considering optimal health with regards to ovary, egg, fertilisation and implantation it is important to consider the entire reproductive and lactation cycle. Particular focus should be placed on the period extending from late lactation through dry period and through to mid- lactation. There are some previously well defined periods that are best illustrated on a time line that can be used as a definition of these periods.
James Husband, Jo Leroy, Mary-Beth Ondarza, Florian Schweigert and Paola Amodeo, joined in debate.
Fig. 1 Diagram over the entire reproduction/lactation cycle representing the primary periods of the cycle and subperiods within each period
Late Lactation
Late lactation cows should be separated into a group for themselves and fed according to the production needs. The purpose is to ensure an optimal body condition score (BCS) when going into the dry period.
In this period it is important to treat the udder with extra care to minimise the risks of mastitis which can affect general health, hereunder ovarian health. Overfeeding should be avoided and the feeding ration should be adjusted to avoid a high BCS when coming into the dry period. Vitamin requirements should be maintained but adjusted for the lower feed intake.
Trying to lower BCS in the dry period can be more detrimental for ovarian health than maintaining a poorly adjusted high BCS upon entering into the dry period from late lactation. If possible concentrates should be removed about one week before drying off to facilitate slowing milk production down. Attempts should be made to avoid the need for BCS adjustment in the dry period. Therefore optimal condition should be achieved in late lactation.
Drying Off
The drying off period is the period in which milking is to be stopped completely and it is also the point in the entire production cycle which is considered optimal to ‘look the cow over’. In this period in which milk production is to be stopped the animal should be fed an extremely low energy diet for 3-5 days, no more, and then be provided with the dry period diet.
Where needed vaccination and antihelminth treatments should be given at this point. Special attention should be given to udder health, since this is a period in which there is increased risk of mastitis. Therefore the udder should be regularly monitored for signs of infection and shed hygiene should be at its optimum so as not to cause an infection.
Hoof health should be monitored and any hoof trimming should be done at this time to ensure optimal hoof conditions in early lactation as well as to avoid any stress that can be caused by the trimming process in early lactation in particular around first service.
Dry Period
The dry period should last on average around 50 days or 7 weeks and can be divided into the Far off period which is generally considered to be the first 4 weeks and the close-up period which is the last 3 weeks.
Far-off Period
In this period the animals should be fed a low energy diet. One strategy that can be used is to dilute the standard ration with good quality chopped straw.
Close-up Period
During this period it is important to continue to provide the animals with a low energy diet, but at the same time try and keep DMI high. This can be done by providing good quality forages and by providing additive such as yeast, essential oils and calcium proprionate.
Special focus should be placed on micronutrient supply so that reserves can be built up. Here antioxidants in the form of vitamin E and beta-carotene are particularly beneficial to help the animal withstand stress influences of the upcoming calving. Micromineral supply should be adjusted by maintaining or slightly lowering calcium intake, increasing magnesium intake and lowering potassium intake.
These adjustments are made to avoid milk fever in early lactation and ensure that the animal mobilises its reserves correctly. Heifers due to calve around the same time should be introduced to this group in this period to facilitate socialisation and reduce the stress of the new environment in the general herd population. Ideally enough space should be provided for these animals of around 10-15m2/cow in a straw yard.
Calving
The most important aspect around calving is hygiene, both for the sake of the cow and for the sake of the calf. In this stressful time for the animal it is important that the cow’s social possibilities are maintained. Providing a calving pen next to the dry group off cows can be beneficial in maintaining social bonds and giving the animal a secure environment in which to calve.
Lactation
Lactation can be roughly divided into ‘fresh’ or early lactation, mid and/or high lactation and late lactation. Late lactation has been dealt with earlier in the cycle and the following will focus on the other groups, in particular the fresh cows.
Fresh Cows
Fresh or transition cows are defined as cows in the first 21 days of lactation. This group of cows is the most important group with regards to monitoring, ovarian health and successful pregnancy. It is this period that the animal is at greatest risk with regards to disease.
During this period ketosis, acidosis, mastitis, metritis and retained placenta are key diseases to watch out for. Therefore it is strongly recommended that this group of cows be kept as a separate group to facilitate monitoring. In particular cow side assays that measure ketones such as β-hydroxybutyrate (BHB) assay can be beneficial in this period. Uterine health should be closely monitored with regards to retained placenta and metritis that can be detrimental to a successful pregnancy at first service.
It is also the period in which the cow has the greatest needs as far as nutrition is concerned. The goal is to increase dry matter intake to match the increased metabolic demands and for this purpose attention must be placed on providing high energy well balanced diets based on high quality forages.
During this period focus should be on sugars/starch which would be more beneficial than Ω3 fatty acids since this is the optimal method to satisfy the cows’ immediate metabolic needs. Once production is well established Ω3 fatty acids can be introduced to support nutritional requirements.
Lastly it is important to record health data from the dry period that can be compared with this period to try and establish where problems arise in the transition period.
