Growth comparison between wild type and slick-haired Puerto Rican Holstein heifers

The present study compared the monthly body weight (BW) of 14 wild type (WT) and 11 slick-haired (SLICK) Puerto Rican Holstein heifers from four to 34 months of age at the Agricultural Experiment Station in Lajas, Puerto Rico. Data were analyzed by the GLIMMIX, GLM and REG Procedures in SAS. Hair coat type and age interacted to affect BW (P=0.0005). However, no differences in BW were observed between WT and SLICK heifers (overall mean BW of 279.33±5.78 and 275.06±6.91 kg, respectively; P=0.3182). From four to 34 months, BW increased in both the WT (93.52±11.42 to 446.35±28.27 kg; P<0.0001) and the SLICK heifers (85.69±9.97 to 381.37±35.81 kg; P<0.0001). The interaction observed between hair coat type and age could be the result of different growth trends, as WT heifers presented a linear curve (BW = 12.28 age + 54.41; R2=0.88; P<0.0001); while their SLICK counterparts showed a quadratic regression (BW = −0.32 age2 + 22.75 age + 6.24; R2=0.74; P<0.0001) between BW and age. These results suggest that SLICK heifers may reach maturity at an earlier age and with less BW. Future studies should evaluate if such differences affect the efficiency and productivity of these animals at maturity.