Browsing by Author "Alward, Kayla Jean"

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    Photoperiod and Temperature-Humidity Index during the Dry-Period Impact Colostrum and Milk Production in Dairy Cattle
    Alward, Kayla Jean (Virginia Tech, 2023-06-26)
    Colostrum quality is critical to calf health as colostrum provides immunoglobulins (Ig) that are critical for a calf's immune system. Despite close management of factors known to affect colostrum production, 23% of dairy cows are still producing inadequate volume or quality of colostrum, which causes calf death and poor performance. Therefore, the objectives of this dissertation are to investigate factors that affect colostrum production and methods to improve colostrum yield and quality. Based on previous literature showing that photoperiod impacts milk yield post-calving in dry cows and that light intensity and temperature-humidity index (THI) impact colostral Ig content, I hypothesized that photoperiod and THI during the dry period impact colostrum yield and quantity in Holstein and Jersey cows. The first study evaluated the isolated effect of photoperiod on colostrum production. Dry cows were housed in a temperature-controlled barn and exposed to either short-day photoperiod (SDPP) of 8 h of light per day or long-day photoperiod (LDPP) of 16 h of light per day for the entire dry period until calving. Altered photoperiod had no effect on colostrum yield, Ig content or other components of colostrum. However, Jersey cows had a higher Brix score, fat, protein, IgA and IgM. After calving, milk production was not affected by photoperiod treatment, likely due to cows being exposed to an irregular lighting scheme. The second study evaluated the combined effects of photoperiod and THI during the dry period on colostrum production and broke cows into a bottom (1), middle (2) and top (3) third based on their photoperiod exposure. Holstein cows produced more colostrum than Jersey cows in each photoperiod category. For both breeds, photoperiod category 1 cows produced less colostrum than cows in photoperiod category 2 and 3. Brix score did not differ by breed but differed by farm and photoperiod category with farm 1, photoperiod category 3 cows having increased Brix score compared to farm 2, photoperiod category 1 and 2 cows. Colostrum components for Jersey cows did not differ by photoperiod category. However, colostrum volume, Brix score, protein and SNF were all impacted by THI and (or) photoperiod variables in predictive modeling. This indicates that colostrum yield and quality in Holstein and Jersey cows are similarly impacted by both photoperiod exposure and THI exposure during the last two months of pregnancy. Therefore, farmers can utilize short-day photoperiod during the dry period during times of moderate THI to improve milk production post-calving without negatively impacting colostrum production. However, future studies are needed to tease out THI and photoperiod impact on colostrum on a large scale in order to improve dry cow management and colostrum production.