Low colostrum yield has recently become a more common complaint from dairy farmers. While it is true that high quality colostrum replacers are readily available today, they are fairly expensive, and thus may be often fed at a dose that is less than optimal. When fed at adequate doses, the cost per calf is significant, and farmers would rather use fresh or stored cow colostrum. There is anecdotal evidence that low energy dry cow diets, season of calving and possibly low energy dry cow diets may affect colostrum volume. There has been quite a bit of research published regarding colostrum quality, but little has been published regarding colostrum quantity.
    In a study published in the January 2019 edition of the “Journal of Dairy Science”, the authors looked at Swedish Red and Swedish Holstein cows with planned 28-day and 56-day dry periods. Both breeds showed lower colostrum yields with the short dry periods. Average colostrum production for all cows in the short dry period group was 6.8 pounds versus 13.4 pounds in the long dry period group. The IgG content of colostrum was not tested, but the colostrum protein levels were higher in the short dry period group, which suggests that IgG levels may have been higher as well. So the amount of colostrum was dramatically reduced, but the quality was likely improved by a short dry period.
    An earlier study, also published in “The Journal of Dairy Science” examined colostrum yield in Jerseys (Gavin, et. al. 2018). This study looked at a variety of factors including, age at calving, male or female calf, dry period length, previous 305ME and milk production, previous lactation length, gestation length and month of calving. The most significant finding was the relationship between month of calving and colostrum yield. The overall colostrum yield was 14.5 pounds in June and only 5.5 pounds in December. That is more than 2.6 times more colostrum for June calving cows than December calving cows. Multiparous cows had a greater decline in colostrum between June and December (14.5 to 2.9 pounds) than first lactation cows (14.3 to 9.24). The authors concluded that the seasonal effect of lower colostrum yield in the winter was due to reduced photoperiod during the month of calving and for the one-month period prior to calving. Length of dry period did also show to be correlated to colostrum volume; a cow having a 45-day dry period was 1.88 times more likely to have insufficient colostrum volume to feed one calf than a cow with a 75-day dry period.
    Little has been published regarding low energy dry cow diets and colostrum volume. A 2016 study (Mann, et. al) showed that cows fed at 100 percent of dietary requirements produced less colostrum than cows fed 125 percent or 150 percent of requirements, but the results were not statistically significant. A sheep study showed that ewes fed 100 percent of NRC produced greater colostrum volume than ewes fed 60 or 140 percent of NRC (Swanson et. al. 2008). Anecdotal reports suggest that providing adequate metabolizable protein when feeding low energy close up diets may also increase colostrum volume.
    Interestingly, the January 2019 edition of JDS also contained a paper (Salfer), examining seasonality of milk, butterfat and protein production. Milk production was up to 7.25 pounds greater on average for milk produced in March, April, or May than milk produced in September, October or November. Fat and protein concentrations peaked in mid-winter and reached a minimum in July. There is some evidence in this paper to suggest that cows in regions with smaller change in photoperiod, e.g. Florida, have less seasonal variation in milk production and protein and fat percentages than cows in northern latitudes. Taken together, the Gavin and Salfer studies suggest that seasonality of milk production and seasonality of colostrum volume are both regulated by photoperiod.
    To sum it up, it looks pretty clear that there is a strong seasonality to volume of colostrum production, and it is due to changes in daylight. Shorter dry periods also appear to result in lower colostrum yields, so farms that have adopted shorter dry periods may see more winter calving cows with inadequate colostrum yield than farms with longer dry periods. Energy and protein levels in prepartum diets have not been proven to affect colostrum yield, but little research exists, so these dietary factors may still be important, too. One cannot easily change the amount of daylight experienced by dry cows on most farms, so the seasonality is something we may have to live with. Farmers who have adopted shorter dry periods might be able to increase colostrum production during the winter by increasing dry period length for winter calving cows.
    Bennett is one of four dairy veterinarians at Northern Valley Dairy Production Medicine Center in Plainview, Minn. He also consults on dairy farms in other states. He and his wife, Pam, have four children. Jim can be reached at bennettnvac@gmail.com with comments or questions.