INFLUENCE OF LENGTH OF DRY PERIOD ON SUBSEQUENT LACTATION IN RAT

Rats given a four-day dry period produced approximately 28 (P < 0.01) and 10% (P > 0.05) heavier litters between Days 8 and 16 of lactation than rats given zero-day or longer (8, 12, or 16 days) dry periods, respectively. On the first day of lactation mammary glands of rats given an eight- or zero-day dry period contained 14% (P < 0.05) more DNA (cell numbers) than glands of rats given other length dry periods. However, on Day 8 or 16 of lactation mammary DNA of rats given zero- or 16-day dry periods was significantly less than DNA of rats given four- or eight-day dry periods. Length of dry period had no detectable effect on RNA/DNA ratios (metabolic activity). Apparently, the effects of dry period length on lactation are associated with factors regulating cell numbers during the subsequent lactation rather than with factors affecting synthetic activity of the remaining mammary cells. Rats given zero- or 16-day dry periods contained less hydroxyproline (collagen) on the first day of lactation than rats receiving the optimal dry period. If collagen is necessary for future mammary development, these lower amounts in zero- and 16-day dry period groups could be one reason these glands contained reduced numbers of cells in later lactation. Dry period length did not affect hexosamine (ground substance) during early lactation, but during late lactation there was a linear increase with increasing length of the dry period. © 1969, American Dairy Science Association. All rights reserved.