Udder Capacity Estimates as Affected by Rate of Milk Secretion and Intramammary Pressure

Abstract

Summary An extra-period Latin-square design balanced for sequence effects, with four groups of five Jerseys each, was used to study udder capacity. A group of five Brown Swiss provided aditional information. Experimental intervals were 8, 12, 16, 20, and 24 hr. in length. The intervals prior to the 8-, 12-, 16-, and 20-hr. experimental intervals were 6, 2, 8, and 4 hr., respectively, and thus too short to affect the experimental results. The 24-hr. interval had preceding intervals of 8, 12, 14, 16, 20, and 24 hr., but they produced no significant effect on total pounds of milk. Sequence effects were not significant. Oxytocin (20 I.U.) was injected before and after each experimental interval to eliminate residual milk effects. From these data, estimates of udder-holding capacity and capacity to secrete against the intramammary pressure and/or the toxin-like action of accumulated milk were obtained. With increasing milking intervals the total pounds of milk increased asymptotically for all groups. The estimated theoretical udder capacities for the five groups of animals in this study were 42.4, 49.9, 55.8, 51.3, and 63.2 lb. of milk. Thirty-five hours was the estimated length of time before milk secretion approached zero. Increases in total milk caused increases in intramammary pressure. With increases in milking interval, total milk, and/or intramammary pressure, both the average and instantaneous secretion rates declined.