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The effect of preservative tablets added to milk on its composition and density is discussed. A comparison between the S.N.F. content of 10-day composite samples of milk from individual herds after making due allowance for added preservative, and the weighted mean S.N.F. calculated on a daily basis, showed that the 10-day composite sample could be used successfully for estimating S.N.F. hydrometrically. A comparison of the weights of S.N.F. supplied when estimated by gravimetric and hydrometric methods was made for ten herds supplying a commercial plant over a period of 260 days. The mean difference was –0·14% of the gravimetrically estimated weight, S.D. 0·4, and the range was ±0·6%. The result is discussed and is considered of sufficient accuracy to justify, on a technical basis, using the hydrometric method of estimating S.N.F. for determining and, if necessary, paying for the S.N.F. supplied.
A within-cow comparison was made of methods of control of udder infection in dry cows whose teats were deliberately contaminated with cultures of mastitis organisms. Very nearly complete protection against infection with staphylococci and streptococci was obtained by infusion of antibiotics through the teat canal. Disinfection alone, i.e. dipping the teats in 2% chlorhexidine, gave good protection against staphylococci but no protection against Streptococcus uberis.