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Physiological implications of liner movement were considered. An artificial teat was used to measure teatcup liner force considered to be massage only when it exceeded atmospheric pressure. Liner force was maximum at the midpoint of the width of the collapsed liner walls and maximum in the middle third of total liner length. Liner force was at least 90% of maximum for 64% of the time the liner was collapsed but reached its maximum only for 8% of the time the liner was collapsed. Pulsated pressure, liner opening and closing, and liner pressure were recorded simultaneously. From this recording, a table was presented with numbers for liner opening pressure, closing pressure, maximum massage, massage time, liner closed time, liner open time, and the product massage×massage time. Some teat end lesions may be explained by observations that the liner collapses in a fixed plane, and liner pressure can vary with lateral teat position and depth of teat penetration. Regardless of the desirability of liner massage, forces on the teat end should be distributed as evenly as possible by routine rotation of the liner within the shell.

This paper fills the need for a simple method for estimating the liner ratio during a pulsation cycle. The method can be used with any liner or shell combination. Ordinary 22-gauge wire was sutured into the inner opposing walls of a teatcup liner. These ``electrodes``were connected to a bridge amplifier, and contact closure was recorded by ultraviolet oscillograph. When the liner walls touched or parted, the resulting signal had the form of a square wave, which allowed precise estimates of liner opening and closing to within 10ms. Additionally, the pulsation chamber pressure was measured and the recording superimposed on the liner opening and closing, thus providing an estimate of the pressures at which the liner walls parted and touched. Liner ratio has been measured by others both by determining the pressure at which the liner walls touched and parted in the absence of pulsations (static) and in the presence of pulsations (dynamic). In an example of the method's usefulness, liner ratio was set by the static method; and three pulsation rates, two ratios, and two liner wall movement speeds were compared for their effects on liner ratio determined by the proposed method (dynamic). At slow liner movement dynamic liner ratio was affected; liner opening pressure was affected more; liner walls remained parted longer. The greatest increase, 9%, occurred at 65 pulsation/min at a static ratio of 70:30. Additional considerations of the method include limitations.

The role of pregastric esterase was investigated in four abomasally-cannulated calves during a sequence of ten 3-day periods beginning when calves were 2 to 5 days of age. Two calves were fed whole milk from nipple bottles to maximize exposure to pregastric esterases, and two other calves were given milk by infusion directly into the abomasum to minimize exposure. The initial system of feeding each calf was continued for eight periods after which treatments were reversed. Postfeeding lipolytic activity of samples of abomasal contents and of intragastric lipolysis of milk fat were markedly greater for orally-fed calves than for abomasally-fed. Systems of feeding effected no significant differences in a) digestibility of dry matter, fat, crude protein, and nitrogen-free extract, b) retention of nitrogen, and c) percentage weight gains. Digestibility of dry matter, crude protein, and nitrogen-free extract of milk and retention of nitrogen were greater in later periods than in initial. Although age of calves was a positive factor associated with utilization of milk, decreased exposure of milk to pregastric esterase and the Resulting reduction of lipolysis in the abomasum did not effect a detectable lowering of milk utilization by calves in age groups studied.

An experiment was conducted to measure the milk production response to increased frequency of milking and to mammary gland stimulation per se. A total of 25 cows was employed in two trials. The treatments compared were twice-daily milking (2 ×), four-times-daily milking (4 ×), and either two-times-daily milking plus hand stimulation without milking (2×H) or two-times-daily milking plus oxytocin injection (2×I) midway between each milking interval. Treatments 2×H and 2×I compared to treatment 2×resulted in a 1.0 to 1.5% nonsignificant increase in production. Treatment 4×resulted in a milk production increase of 7.9% over treatment 2 ×. Further, this increase was attained by the second day on the increased milking frequency. The rapidity of the production response, plus the lack of response to additional stimulations per se, suggests that stimulation→oxytocin→prolactin→increased milk synthesis is not the explanation. Rather, that frequent milking→reduced intramammary pressure→increased secretion is probably the explanation.

Twenty-four primiparous mice were divided into four equal groups. The four groups were randomly assigned to injections of .5, .25, and .125 IU of synthetic oxytocin or oxytocin solvent. Average daily body weights of mothers and pups were compared over 15 days postpartum. Mammary glands were removed and processed for histological examination. Average body weight gains of mothers were not significantly different among treatment groups. In general, there was no difference in average body weight gain of pups among treatment groups except that in the group nursing mothers injected with .5 IU oxytocin, average weights decreased slowly until by 12 days of age their weight gain adjusted for 4-day weights was less than the .25 and .125 oxytocin groups (P Milk production response to exogenous oxytocin injection is dependent both on amount of oxytocin administered and on duration and intensity of the suckling stimulus applied.

Summary Forty-eight animals from a Streptococcus agalactiae -free herd, after a 4-week standardizing period immediately after calving, were assigned to be milked from the fifth to the 44th week of lactation at either 10, 13.5, or 17 in. of vacuum and for a "normal" or "twice normal" duration. Of these animals, 24 were Guernseys and 24 Holsteins. Within each breed group, 12 were first-calf heifers and 12 had one or more previous lactations. Within each breed-lactation group of 12, six were selected for being "clean" of mastitis and six for being "infected." The following results were obtained: 1.No appreciable differences in milk yield and FCM were observed between vacuum levels. Milking time and time to reach peak rate of flow decreased in a linear manner and rate of milk flow increased. The least amount of time spent in stripping was at the 13.5 in. vacuum level, and the least amount of strippings, expressed as a percentage of the total yield, was at the 10-in. level. 2.Leaving the milking machine on the udder for an extended duration (twice normal) resulted in slightly greater yields of FCM (1.01b. per cow per day) and decreased stripping time. 3.In this experiment, mastitis infected animals gave greater milk yields and had slower rates of milk flow than did the mastitis clean animals. 4.The differences between first-calf heifers and animals with one or more lactations and between Guernseys and Holsteins agreed in general with previously published studies.

Eighteen primiparous mice in their 6th to 9th day of lactation were randomly divided into groups of six. Each group was assigned to one of the three milking intervals, .25, 4, and 12h. Blood flow was measured simultaneously in right and left abdominal mammary glands by Sapirstein's indicator fractionation technique with sodium 24 chloride as the indicator. Lactose was extracted from the same tissue and quantified by gas chromatography. Up to 4h, mammary blood flow was inversely related to the amount of milk accumulated in mammary gland. Around 4h blood flow started to level off and somewhere between 4 and 12h reached a maintenance rate. Rate of lactose synthesis was markedly reduced in this period. The relationship between mammary blood flow (Y) and lactose content (X) in the tissue was curvilinear, Y=4.43 − .83X + .06X 2 (correlation – .83).

The use of ultrasound for locating and identifying structures in the lactating mammary gland was explored. A method was outlined for using ultrasound. Internal mammary gland measurements were taken at two different locations; i.e., Spots 1 and 2 being one-third and two-thirds the distance from the floor to the top of the udder, respectively. Change in quarter width as well as median width and gap were compared under five stimulative states—i.e., prestimulation; post-stimulation, premilking; post-normal milking; post-oxytocin injection, precomplementary milking; and post-complementary milking. Sonograms were presented which identified the skin, median and lateral suspensory ligaments, milk ducts, and supramammary lymph nodes. Some general observations were reported on the relation among quarter width, intramammary pressure, and quarter milk production, using limited data. It was shown that following a complete milking, the milk ducts are probably collapsed. The feasibility of using ultrasound to visualize internal structures and measure their responses to vary physiological conditions was demonstrated.

The primary purpose of the present trial was an attempt to produce antibodies to autologous and homologous milk whey proteins in three ruminant species; moreover, to use rabbits as a source of heterologous antibody and to show that the preparation used for immunization was antigenic. The underlying thought was that since milk proteins are unique to the mammary gland, an auto-allergic condition to milk proteins may play a role in mastitis. Lactating females, virgin females, and males of the bovine, ovine, and caprine species were immunized with injections of a mixture of complete Freund's Adjuvant and whole milk. Eleven injections were given over a three-month period. The results showed the bovine did not produce antibodies to either homologous or autologous milk proteins. However, the ovine and caprine species produced both autologous and homologous antibodies of low concentration. Neither quarter milk production nor incidence of clinical mastitis was influenced by repeated injections of milk. It was concluded that the autologous and homologous antibodies produced against milk proteins were not important etiological agents in an auto-allergic condition of mastitis. It was postulated that the apparent unresponsiveness to injected milk proteins in the bovine may be due to intestinal absorption of large quantities of immunologically reactive milk proteins during the first few neonatal days. This, then, could cause an acceptance of milk proteins and failure to recognize these as being foreign in later life.

Estradiol-testosterone injection had similar lactation suppressing effects in sheep, goats and cattle. The depression in milk production was generally in proportion to the dose, although the extent and duration was influenced by individual animal characteristics. Cows and goats responded within three days, whereas, sheep required eight days for maximum depression. The net synthesis of fat, protein and solids-not-fat following injection was reduced. As expected, when milk production decreased, solids-not-fat and generally per cent protein increased, whereas, fat was somewhat more erratic and generally depressed. A stimulatory effect of the hormone on milk synthesis following the initial depression was evident. In subsequent lactations, there was no altered production. In addition, the milk was colostrum-like following smaller injections and was markedly altered (watery, clotted, etc.) following larger injections. The physical appearance was accompanied by relative increases in all whey proteins derived from blood (two times for albumin, and 20 times for immune and β 2 -globulins). Those synthesized in the mammary gland decreased to one-third for α -lactalbumin and to one-half for β -lactoglobulin. Possible effects of estrogen on suppressed lactation and altered composition during pregnancy were considered. Visible changes in the appearance of milk suggested that normal variations in endogenous hormone levels, especially during the estrous cycle, may influence milk leucocytes to a great extent.