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. / Doctor of Philosophy / Cows do not transfer antibodies or immunoglobulins to their offspring during gestation and calves are born deficient in antibodies that are critical for a healthy immune system. Instead, cows transfer antibodies into the first milk that they produce, termed colostrum. After calves ingest the colostrum, the antibodies are absorbed by the small intestine and enter circulation where they can traverse the body to identify and neutralize pathogens. To ensure adequate immune system function, calves must ingest 150 – 200 g of antibodies within 6 h of birth. However, around 23% of cows do not produce enough antibodies in their colostrum or have low colostrum yield overall. 19% of calves do not ingest enough antibodies and will die or have negative health effects that persist into adulthood as a result.
Therefore, the objective of this dissertation is to investigate methods to improve colostrum production in cows to improve calf health and reduce calf deaths. While several factors that affect colostrum production have been identified and are managed for optimum colostrum production, there is still high variation in colostrum production from cow to cow. Based on previous research showing that colostrum yield varies seasonally and that daily light exposure, or photoperiod, can impact milk production, I hypothesized that photoperiod and temperature-humidity index (THI) during the last two months of pregnancy impact colostrum production in cows.
The first study was designed to isolate the effect of photoperiod on colostrum, by housing Holstein and Jersey cows in a temperature-controlled barn during the last two months of pregnancy and exposing them to varying daylengths. Cows were exposed to either a short-day photoperiod of 8 h of light per day or a long-day photoperiod of 16 h of light per day. When the cows gave birth, they were milked and the amount of colostrum produced and the components of the colostrum were evaluated. A Brix refractometer, which is widely used by farmers to estimate colostrum quality as it is an on-farm tool that estimates colostrum antibody content, was also used in this study. Cows were returned to ambient photoperiod and milk, fat and protein production were tracked for 15 weeks. I found that altered photoperiod had no effect on colostrum yield, antibody content or other components of colostrum. However, Jersey cows had a higher Brix score, fat, protein, antibody IgA and antibody IgM. After calving, milk production was not affected by photoperiod treatment, likely because of irregular lighting exposure after calving. These data indicate that photoperiod alone may not be causing the seasonal variations associated with colostrum production.
Therefore, a second study was conducted to evaluate the effects of photoperiod and THI together on subsequent colostrum production in Holstein and Jersey cattle by month. Colostrum production and weather data were collected for cows housed in ambient photoperiod and THI for the last two months of pregnancy from two different farms. Cows were divided 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.
Data from these studies are the first to show the isolated effect of photoperiod on colostrum production in Jersey cows and the second showing data on Holstein cows. Recommendations have already been made to dairy producers to limit photoperiod exposure during the last two months of pregnancy in order to increase milk production post-calving. This study shows that limiting photoperiod will not compromise colostrum production in cows. However, I also found that colostrum production is also impacted by THI exposure and that colostrum yield and quality have inverse relationships with photoperiod and THI exposure. Whereas colostrum yield increases with increased photoperiod and THI, Brix score decreases. Therefore, managing for increased colostrum quality is compromised by colostrum yield. This study also found that the widely accepted indirect measure of antibody content, the Brix score, was not a reliable estimate of antibody content and instead, a better indicator of solids content of colostrum.
In conclusion, these data show that photoperiod alone does not impact colostrum production, rather a combined effect of photoperiod and THI are responsible for seasonal variation in colostrum and differences between breeds of cow are also evident. In addition, Brix score may not be the best indicator of colostrum quality and could be replaced by more reliable methods by dairy farmers to ensure that adequate colostrum is fed to calves. Future studies will need to explore differences in response to photoperiod vs. THI alteration and explore genetic associations with colostrum production, to identify which genes are associated with increased colostrum quality in Jersey cows so that we may genetically select for increased colostrum quality.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/115513 |
| Date | 26 June 2023 |
| Creators | Alward, Kayla Jean |
| Contributors | Dairy Science, Cockrum, Rebecca R., Ealy, Alan Dale, Petersson-Wolfe, Christina Sonja, Dahl, Geoffrey Eliot |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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