Dairy Husbandry 



Persistency of Milk Yield Is Influenced by Certain Factors. 



Persistency of milk production at a high level is considered to be a 

 desirable attribute of a dairy cow. Among dairymen, there is considerable 

 difference of opinion regarding the factors that influence persistency. Age, 

 inheritance or heredity, season of freshening, methods of feeding, and even 

 the breed have been assumed to influence separately or collectively the per- 

 sistency of milk yield during a lactation. The availability of daily milk 

 weights for all cows in the University of New Hampshire herd over a period 

 of approximately 20 years offered an opportunity to study the relation of 

 certain factors to persistency of milk production. 



Thirty-one Holsteins, each with 4 lactations, were used in the study. 

 Persistency factor was computed by relating milk yield (F.C.M. basis) for 

 subsequent 10-day periods from the 30th to the 210th day of the lactation. 



Persistency was found to be significantly influenced by peak yield. After 

 correcting for the influence of peak there was a significant difference favor- 

 ing fall freshening in comparison with each of the other three seasons. There 

 was some advantage in persistency for winter freshening over summer. Age 

 was found not to be a significant factor. There was a correlation between 

 the first and second lactation only. 



K. S. Morrow 



Sex Ratio in Dairy Cattle Is Not Influenced by 

 Normal Herd Management Practices. 



If the sex ratio in dairy cattle could be controlled, an important phase 

 of the herd replacement maintenance problem would be solved. Countless 

 theories of sex control have been suggested. To study the normal relation of 

 certain herd management practices to sex ratio, data were analyzed on 1557 

 births in the University of New Hampshire dairy herd. 



The over-all ratio of 94.0 males to 100 females was in contrast to ratios 

 normally reported for dairy cattle in favor of males over females. 



Season of the year at conception, age of sire and dam, gestation number, 

 number of services, length of gestation, and length of calving interval were 

 found to have no significant influence on sex ratio. 



K. S. Morrow 



The Vitamin D Content of Forage Varies Greatly. 



A study was started several years ago to determine whether milking 

 cows maintained under New Hampshire farm conditions need supplemental 

 vitamin D. It was soon found that the first problem was to learn more about 

 the vitamin D content of the common forages the cows eat and the factors 

 which affect it. As a result, such a study covering a period of four years was 

 carried out. 



The results of the study show that the vitamin D content of forage 

 varies widely depending on a number of factors. The vitamin D content of 

 first-cutting forage harvested at the generally recommended stage of ma- 

 turity was generally low when mowed and it could not be increased greatly 

 by ultraviolet irradiation. Similar second-cutting forage was often higher in 



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