Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Animal Science

Major Professor

Agustin G. Rius

Committee Members

Travis Mulliniks, Lannett Edwards, Peter Krawczel


Heat stress (HS) causes decreases in production of lactating cattle that is only partially explained by decreases in intake. Evidence suggests that changes in energy and protein metabolism occur to cope with the impact of HS. The objective of this thesis was to determine if the effect of jugular infusion of essential amino acids (AA) ameliorated the negative effects of HS in milk production and metabolism. Twelve multiparous lactating Holstein cows were used in a crossover design to evaluate the effect of thermoneutral (THN) and HS environments along with the absence (CTL) or presence (ML+BCAA) of essential AA infusion. Infusions consisted of methionine (12 g), lysine (21 g), leucine (35 g), isoleucine (15 g), and valine (15 g) per day. Thermal treatments were imposed from days 1 to 14 and jugular infusion of AA from days 7 to 14. Milk and blood samples were collected on days 5 to 7 and 12 to 14. Data were analyzed using the Mixed procedure of SAS and reported as least square means ± [plus or minus] standard error of the mean. Temperature humidity index (THI) values during THN never exceeded 66, whereas THI values during HS peaked at 76 and were above 68 for 14 h/d. Compared with the CTL treatment, ML+BCAA treatment increased rectal and vaginal temperatures in the HS treatment by 0.5 and 0.4°C respectively, but did not increase temperatures in the THN treatment (interaction P < 0.05). Heat stress decreased (P < 0.05) DMI (17.4 vs 18.9±0.41 kg/d), milk yield (29.3 vs 32.1±1.09 kg/d), milk protein percentage (2.95 vs 3.06±0.06%), and milk protein yield (0.87 vs 0.98 ±0.05 kg/d). The ML+BCAA treatment had no effect on milk and milk protein yield but increased (P <0.001) milk protein percent (3.04 vs 2.96±0.06%). Heat stress elicited expected decreases in production, while the infusion of AA increased milk protein percent indicating a possible improvement of protein synthesis. However, the rise in rectal temperatures due to infusion is a cause for concern.

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