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Late pregnancy and the first 60 days post calving is a high-stress period for dairy cows. During this period, cows have a tendency to lose body condition and be more vulnerable to changing climatic conditions, resulting in an increased susceptibility to disease and a reduction in milk production. The VGX Animal Health plasmid-mediated growth hormone releasing hormone (GHRH) was evaluated in dairy cows for its potential to mitigate heat stress and its effects on the morbidity, mortality and milk production of treated animals and their offspring. A single treatment in the third trimester of pregnancy was given to 32 of 52 heifers, while 20 heifers remained as controls. Body condition scores of treated animals vs. controls were statistically significantly better (3.55 vs. 3.35 at 60-80 days in milk (DIM), P < 0.0001). Hoof pathology was reduced with treatment. Involuntary culling of treated animals was reduced by 40%. Mortality of heifers was significantly decreased (3% vs. 20% in controls, P < 0.003), while calves from treated heifers were 25% less likely to die at birth (18.8% vs. 25%), and from birth-to-260 days (0% vs. 20%). Overall calf mortality was reduced by 47%, P < 0.02. Calves from treated heifers were heavier at 260 days post-natal (P < 0.05). Milk production was increased by 10 to 22% (27.45 ± 0.89 kg/d vs. 23.2 ± 1 kg/d) in GHRH-treated animals compared to non-treated controls up to 300 DIM. The immune enhancing effects were also studied in this same group of animals. At 18 days post treatment, the GHRH-treated animals had increased numbers of CD2+ αß T-cells (P <0.004), CD25+CD4+ cells (P <0.0007), and CD4+CD45R+ cells (P < 0.016) compared to controls. These increases were maintained long term after treatment and correlated with plasmid expression. At 300 days post treatment CD45R+/ CD45RO- naive lymphocytes were significantly increased in frequency (P < 0.05). Natural killer lymphocytes (CD3-CD2+) were also increased. Collectively, these results indicate that the myogenic GHRH-expressing plasmid was successfully electrotransferred during the third trimester of pregnancy and resulted in greatly improved production, viability and general welfare of dairy cattle exposed to a four month period of high temperatures and humidity during late gestation and calving. |
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