Date of Award

Fall 2014

Degree Type


Degree Name

Master of Science (MS)


Animal Science

First Advisor

Tamilee D. Nennich

Committee Member 1

Michael M. Schutz

Committee Member 2

Keith W. Johnson

Committee Member 3

Michael Neary


Reduced heat stress and lower gastrointestinal parasite loads can increase growth rate in heifers, potentially reducing the age at first breeding and lowering the costs associated with raising replacement dairy heifers. Providing shade is a recommended practice for reducing heat stress of grazing animals and is considered important for their wellbeing and productivity. However, limited information is available on the growth performance of young grazing dairy heifers when they are provided shade. Likewise, numerous products exist to prevent gastrointestinal parasites in animals. The development of new anthelmintic products, such as LongRange® (eprinomectin), increase the need for research to help understand the effects of these products on growth rates and fecal egg counts (FEC) in post-weaned dairy heifers. Studies were conducted to evaluate management strategies for reducing heat stress and parasite loads in pre-pubertal grazing dairy heifers. The objectives of these studies were: Study 1) to determine the effects of shade on the growth performance of grazing Holstein dairy heifers throughout the summer months, and Study 2) to compare the effect of eprinomectin (LongRange ® ) and doramectin (Dectomax® ) on weight gain, structural growth, and FEC of post-weaned dairy heifers grazed over the summer months.

In study 1, 76 (n = 44 in 2012 and n = 32 in 2013) Holstein heifers were randomly assigned to 1 of 4 groups according to BW (163.8 ± 7.27 kg, 150.6 ± 8.5 d age). Groups were assigned to 1 of 2 treatments: no shade (NOSHADE) or 1.7 m2 shade/heifer in 2012 and 2.3 m2 shade/heifer in 2013 (SHADE). In study 2, 48 Holstein heifers were randomly assigned to 1 of 12 groups according to BW (169.5 ± 8.5 kg, 149.8 ± 13.8 d of age) in 2014. Groups were assigned to 1 of 2 treatments: 1) treated with injectable eprinomectin (LongRange ® ) (LGR) or 2) treated with injectable doramectin (Dectomax® ) and pyrethroid impregnated fly tags (DFT). Body weight (BW), hip height (HH), withers height (WH), hip width (HW), body condition score (BCS), and heart girth (HG) were measured every 4 weeks in all years. Rectal temperatures were collected every 4 weeks in study 1. Blood samples were collected for plasma urea nitrogen (PUN) analysis in all years. The duration of the studies were from May until September in years 2012 and 2013 and from May until August in year 2014. For study 2, individual fecal samples were collected for FEC and fly counts were determined. Data on water intake was collected in 2013 and 2014. Temperature and relative humidity were recorded using data loggers in all years. Data were analyzed using PROC MIXED in SAS. Growth data were analyzed as repeated records with paddock as the experimental unit.

Providing shade during the summer months or treating for gastrointestinal parasites did not change BW (P = 0.72) and (P = 0.70), respectively. The ADG was similar between the treatments in both studies. Skeletal measurements, including HH, WH, HW, and HG, were similar both in study 1 (P = 0.25) and in study 2 (P = 0.34). In study 1, when data were compared by year, BW and ADG were similar between years (P = 0.27). Skeletal measurements including HH, WH, HG, and HW were different between the years (P < 0.01). The BCS and rectal temperatures were different between the years (P < 0.01), but no treatment differences were detected (P < 0.85). Temperature loggers recorded lower average ambient temperatures in SHADE compared to NOSHADE in both 2012 (32.1 and 33.1°C, respectively) and in 2013 (27.7 and 28.7°C, respectively) during mid-day (1200 to 1500 hr). Providing shade did not improve the growth performance of Holstein dairy heifers in study 1. In study 2, heifers receiving LGR had lower FEC (P = 0.02). In contrast, heifers treated with DFT tended to be lower in count of horn flies (P = 0.08). Water intake and face fly counts were similar between the treatments (P = 0.24). The two parasite control products had similar effects on growth of post-weaned dairy heifers; however, the LGR treatment reduced FEC and the DFT treatment reduced horn flies.