Dry cows need cooling too in summer

Summer losses in milk production are usually related to the negative impact of summer heat stress on the lactating cow. Actually, this is true, due to the large negative effect of heat stress on feed consumption and the efficiency of feed utilization of the lactating cow, as well as on reproductive traits. Recently, it was found that also dry cows, although they are not producing milk, are negatively affected when subjected to heat stress conditions, mainly, due to lower milk and milk solids production in early subsequent lactation, higher incidences of diseases (due to reduce immune function) and metabolic disorders and poor fertility traits, all occurring after calving and in early stages of subsequent lactation, although occurring in autumn and early winter, when heat stress is already over.

First publications describing the negative summer effect on late pregnant cows appeared in the seventies in Florida. In these days, milking cows were kept there in “Corral” shelters with limited access to shade, when dry cows were kept outdoor, with no shade at all. Florida “Herd Book” data showed that cows calving in late summer and autumn produced near 15% less milk in their subsequent lactation as compared to those calving in the winter. Researchers from Gainesville, Florida showed that dry cows, provided with shade during the dry period gave birth to heavier calves and produced 5% more milk in early stages of subsequent lactation, as compared to dry cows without any shade at all (1). The birth of heavier calves obtained in this study can probably be related to better blood flow (as well as hormones and nutrients) to pregnant cow’s uterus (as cows do not need to spread more blood to cow’s surface as cooling a mechanism). It was confirmed that heavier calves and their placentas (as was detected in other studies), is related to better hormonal induction of the development of the mammary tissue (fetal and placental hormones are responsible to the renewal and cells proliferation of mammary tissue before calving), leading to better preparation of the udder for lactation and therefore, increasing milk output in early stages of subsequent lactation.

Based on the experience gained in the seventies in Florida, and due to the fact that dry cows in Israel are usually provided sufficient shade, we decided in the mid-eighties, to investigate the effect of cooling dry cows by a combination of wetting and force ventilation (as we did with milking cows), on offspring weight and cows milk production in subsequent lactation. In the control group, identical cows were provided only shade (2). Calves weight and average daily milk production in the first trimester of lactation are described in Table 1.

Table 1 – Calves birth weight (kg) and average daily milk production (kg), in first 150 days of lactation in cooled dry cows, as compared to cows provided only shade.