Effects of Bovine Somatotropin on Dry Matter Intake, Milk Yield, and Body Temperature in Holstein and Jersey Cows During Heat Stress1 J.
w.
WEST,2 B. G. MULLINIX,3 and J. C. JOHNSON, JR.2 University of Georgia Coastal Plaln StaIlon llftan 31793
K. A. ASH and V. N. TAYLOR The Upjohn Company
Kalamazoo, MI 49001 ABSTRACT
score. Greater heat stress was associated with the higher milk production of cows administered bST. (Key words: bovine somatotropin, heat stress, lactation)
Thirty-one lactating Holstein and Jersey cows were used to detennine the effect of daily injections of 0 or 20 mg of recombinant bST in hot, humid weather. The comparison period lasted 80 d, from mid-June through August. The maximum and minimum ambient temperature and relative humidity averaged 34.6 and 22.2·C and 100 and 59.8%, respectively. Body temperatures of somatotropintreated Holsteins were elevated over controls by .2 and .3·C at the a.m. and p.m. milkings, respectively, whereas corresponding treabnent effects for Jerseys were .5 and .6·C, thus demonstrating a breed by treatment interaction. The response of milk and FCM yields and apparent efficiency of production to somatotropin administration depended on the level of production prior to treatment. Cows at low pretreatment production increased milk and FCM yields to a greater degree than did cows at higher production. A breed by treatment interaction showed that Holsteins increased milk and FCM yields more than Jerseys upon administration of somatotropin. Intake of OM was not affected by treatment. Cows administered bST lost BW and condition
INTRODUCTION
Received January 16, 1990. Accepted May 9. 1990. lSupportcd by Hatch and stale funds allocated to the Georgia Agricultural Experimmt Station and by The Upjohn Company. 2Department of Animal Science. 3Statistical and Computer Services. 1990 J Dairy Sci 73:2896-2906
Many cows located in the southern regions of the United States are subject to high ambient temperatures and relative humidity (RH) for several months each year, and cows in other regions may experience short, intense periods of heat stress. Exaggerated heat stress produced by exposing cows to direct sunlight caused OM intake to decline 15% and milk yield to decline 22.7% (11). Johnson et al. (9) reported that milk production and TON consumption declined as the temperature-humidity index increased. They also estimated that for each .55·C increase in body temperature above 38.6·C, a 1.8-kg decline in milk yield occurred. Reduced feed intake probably is a protective mechanism by which a cow reduces metabolic heat production. Depressed intake reduces heat production associated with digestion and metabolism (24). Numerous studies have demonstrated the efficacy of recombinant bST (rbST) for improvement of milk yield, OM intake, and gross efficiency of production (3, 5, 17, 20). However, the effects of rbST and heat stress on milk production potentially are antagonistic. Cows administered pituitary-derived bovine somatotropin (pbST) during heat stress (28.9·C, 55% RH) in environmental chambers increased milk yield 3.9% over cows exposed to heat stress alone (12). Feed intake declined 5.8%, but reetal temperature was not altered with
2896
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SOMATOTROPIN USE IN HOT, HUMID WEATHER
pbST use in the hot environment. Staples et al, (21) reported increased milk. yield but no change in DM intake or body temperature when pbST was administered to cows during August in Florida. However, Zoa-Mboe et al, (27) reported slightly higher body temperatures in cows administered rbST during hot weather. This was associated with increased FCM yield (9.2%) and no change in DM intake. Increasing environmental temperature decreases the efficiency of radiation and conduction of body heat to the environment and increases the reliance of the cow on evaporative cooling through sweating and panting (10). However, high humidity reduces the rate of evaporation, thus hindering evaporative cooling. Johnson et al. (9) showed an inverse relationship between milk production and body temperature. The objectives of our study were: 1) to determine how rbST affects DM intake and milk production in lactating Holstein and Jersey cows; 2) to examine the effects of rbST on cow body temperature; and 3) to measure the effects of rbST on apparent efficiency of production, BW, and body condition score when used in a hot, humid environment. MATERIALS AND METHODS
Thirty-four multiparous lactating cows (16 Holstein, 18 Jersey), with average days in milk (DIM) of 182 (Holsteins, 187 DIM; Jerseys, 178 DIM) at the beginning of the study, were used to determine the effects of rbST in a hot, humid climate. Three cows (2 Holstein, 1 Jersey) were removed from the study; one because of sore feet, one because of severe mastitis, and one because of its inability to operate the magnetic gate feeder. Thus, 31 cows completed the study. This study was conducted at the Coastal Plain Experiment Station in southern Georgia, which is situated at 31.45° north latitude and 83.517° west longitude. Management
Cows were housed in free stalls covered with sloping metal roofs. The roof covered only the free stalls and adjacent feed areas, and the area over the concrete traffic alleys was uncovered. All cows had access to shade, but they had no additional mechanical cooling.
Cows were adapted to the basal ration and were trained to use magnetic gate feeders (American Calan, Northwood, NH) during a 19-
w.
WEST,2 B. G. MULLINIX,3 and J. C. JOHNSON, JR.2 University of Georgia Coastal Plaln StaIlon llftan 31793
K. A. ASH and V. N. TAYLOR The Upjohn Company
Kalamazoo, MI 49001 ABSTRACT
score. Greater heat stress was associated with the higher milk production of cows administered bST. (Key words: bovine somatotropin, heat stress, lactation)
Thirty-one lactating Holstein and Jersey cows were used to detennine the effect of daily injections of 0 or 20 mg of recombinant bST in hot, humid weather. The comparison period lasted 80 d, from mid-June through August. The maximum and minimum ambient temperature and relative humidity averaged 34.6 and 22.2·C and 100 and 59.8%, respectively. Body temperatures of somatotropintreated Holsteins were elevated over controls by .2 and .3·C at the a.m. and p.m. milkings, respectively, whereas corresponding treabnent effects for Jerseys were .5 and .6·C, thus demonstrating a breed by treatment interaction. The response of milk and FCM yields and apparent efficiency of production to somatotropin administration depended on the level of production prior to treatment. Cows at low pretreatment production increased milk and FCM yields to a greater degree than did cows at higher production. A breed by treatment interaction showed that Holsteins increased milk and FCM yields more than Jerseys upon administration of somatotropin. Intake of OM was not affected by treatment. Cows administered bST lost BW and condition
INTRODUCTION
Received January 16, 1990. Accepted May 9. 1990. lSupportcd by Hatch and stale funds allocated to the Georgia Agricultural Experimmt Station and by The Upjohn Company. 2Department of Animal Science. 3Statistical and Computer Services. 1990 J Dairy Sci 73:2896-2906
Many cows located in the southern regions of the United States are subject to high ambient temperatures and relative humidity (RH) for several months each year, and cows in other regions may experience short, intense periods of heat stress. Exaggerated heat stress produced by exposing cows to direct sunlight caused OM intake to decline 15% and milk yield to decline 22.7% (11). Johnson et al. (9) reported that milk production and TON consumption declined as the temperature-humidity index increased. They also estimated that for each .55·C increase in body temperature above 38.6·C, a 1.8-kg decline in milk yield occurred. Reduced feed intake probably is a protective mechanism by which a cow reduces metabolic heat production. Depressed intake reduces heat production associated with digestion and metabolism (24). Numerous studies have demonstrated the efficacy of recombinant bST (rbST) for improvement of milk yield, OM intake, and gross efficiency of production (3, 5, 17, 20). However, the effects of rbST and heat stress on milk production potentially are antagonistic. Cows administered pituitary-derived bovine somatotropin (pbST) during heat stress (28.9·C, 55% RH) in environmental chambers increased milk yield 3.9% over cows exposed to heat stress alone (12). Feed intake declined 5.8%, but reetal temperature was not altered with
2896
2897
SOMATOTROPIN USE IN HOT, HUMID WEATHER
pbST use in the hot environment. Staples et al, (21) reported increased milk. yield but no change in DM intake or body temperature when pbST was administered to cows during August in Florida. However, Zoa-Mboe et al, (27) reported slightly higher body temperatures in cows administered rbST during hot weather. This was associated with increased FCM yield (9.2%) and no change in DM intake. Increasing environmental temperature decreases the efficiency of radiation and conduction of body heat to the environment and increases the reliance of the cow on evaporative cooling through sweating and panting (10). However, high humidity reduces the rate of evaporation, thus hindering evaporative cooling. Johnson et al. (9) showed an inverse relationship between milk production and body temperature. The objectives of our study were: 1) to determine how rbST affects DM intake and milk production in lactating Holstein and Jersey cows; 2) to examine the effects of rbST on cow body temperature; and 3) to measure the effects of rbST on apparent efficiency of production, BW, and body condition score when used in a hot, humid environment. MATERIALS AND METHODS
Thirty-four multiparous lactating cows (16 Holstein, 18 Jersey), with average days in milk (DIM) of 182 (Holsteins, 187 DIM; Jerseys, 178 DIM) at the beginning of the study, were used to determine the effects of rbST in a hot, humid climate. Three cows (2 Holstein, 1 Jersey) were removed from the study; one because of sore feet, one because of severe mastitis, and one because of its inability to operate the magnetic gate feeder. Thus, 31 cows completed the study. This study was conducted at the Coastal Plain Experiment Station in southern Georgia, which is situated at 31.45° north latitude and 83.517° west longitude. Management
Cows were housed in free stalls covered with sloping metal roofs. The roof covered only the free stalls and adjacent feed areas, and the area over the concrete traffic alleys was uncovered. All cows had access to shade, but they had no additional mechanical cooling.
Cows were adapted to the basal ration and were trained to use magnetic gate feeders (American Calan, Northwood, NH) during a 19-
