An average body dimension in the sense of the wight then it is different in different breed wise, for example indian cattle have b.wt abt 400-550 kg and exotic cattle have 800-1000kg. In that also different breed wise and locality wise weights are different. If we consider surface area of cow then read this article  http://naldc.nal.usda.gov/download/IND43967149/PDF 

heat production:

average body temt of cow is 99 - 101.5 F

thank you sir

One thing important to remember is that heat production varies according to the environment, feeding pattern, type of diet offered to the animals.

Like Ramesh said, Bos indicus cattle usually will be lighter (Nellore, Brahman) compared with Bos taurus (or european breeds; Hereford, Angus)