MAMMARY
GLAND
GROWTH
IN S H E E W
R. R. Anderson 2 ,3 Ruakura A n i m a l Researcb Centre, Hamilton, New Zealand and University o f Missouri 4 , Columbia 65201
SUMMARY
INTRODUCTION
Development of m a m m a r y glands was assessed in Romney and Romney-cross sheep. Animals were slaughtered at birth + or - 5 days, at 3, 4 and 5 months, at the beginning of pregnancy (2 to 3 days after mating), at the end of pregnancy (140 to 148 days pregnant) and at 5 days lactation. Mammary glands were weighed before and after trimming and the trimmed glands were extracted with lipid solvents. The remaining dried fat-free tissue (DFFT) were weighed and ground. Nucleic acids and nitrogen were measured. Based upon wet weight changes, 25% of growth occurred prior to pregnancy, 55% during pregnancy and 20% during early lactation. When DFFT was evaluated, the increases were 20% from birth to the beginning of pregnancy, 80% during pregnancy and none in early lactation. Percent protein paralleled DFFT changes among groups. However, when DNA, the most realistic measure of mammary growth, was considered, the percentages of development were 20% from birth to the start of pregnancy, 78% during pregnancy and 2% during early lactation. The ratio of RNA to DNA remained near 1 from 3 months of age to the end of pregnancy and increased to 1.7 in early lactation. Unlike many small laboratory species, the sheep does not experience any appreciable post-parturient 'lactational' growth of the mammary gland.
Growth of mammary glands in mammals has been measured by anatomical and biochemical methods with reasonable success. Relative amounts of growth during various phases in the female's development have been determined in several laboratory species in order to establish bases for experimentation of hormonal stimuli concerned in mammary gland growth. Those studies which have incorporated in them the determination of nucleic acids as indices of mammary cell numbers and relative cellular activity have included mice (Brookreson and Turner, 1961), hamsters (Sinha et al., 1970) and rabbits (Lu and Anderson, 1973). Limited research has been directed toward domestic species, including cattle (Tucker et al., 1973), swine (Hacker and Hill, 1972) and sheep (Denamur et al., 1972), in which nucleic acid changes during early lactation were studied. The present study considers mammary gland growth in sheep from birth, through puberty and pregnancy, to early lactation with the aim of establishing a basis for recommendations in management and nutrition, as well as experimentally stimulating mammary growth by various hormone regimes.
(Key Words: Mammary Gland, Growth, Sheep.)
MATERIALS AND METHODS Female sheep of the Romney breed or Romney-crosses with Southdowns or Border Leichesters were used in this study. They were taken to the abattoir at Ruakura Animal Research Centre and slaughtered. Groups and numbers per group were as follows:
1Contribution from the Missouri Agricultural Exa. fetuses from 140 to 148 days pregnancy periment Station. Journal Series No. 7111. Approved or lambs 5 days old (n = 10) by the Director. 2Work conducted while author was a Senior b. 3-month-old lambs (n = 30) Fulbright Research Fellow in New Zealand. c. 4-month-old lambs (n = 30) 3The author expresses his gratitude to W. G. d. 5-month-old lambs (n = 27) Whittlestone for use of his laboratory and to A. e. beginning (day 2 to 3) of pregnancy (n = Pearson and R. Findlay for their assistance. 4Department of Dairy Husbandry. 20) 118 JOURNAL OF ANIMAL SCIENCE, Vol. 41, No. 1, 1975
Downloaded from https://academic.oup.com/jas/article-abstract/41/1/118/4668118 by Washington University in St. Louis user on 06 August 2018
MAMMARY GLAND GROWTH IN SHEEP f. late (day 140 to 148) pregnancy (n = 19) g. early (day 5) lactation (n = 17). Ewes comprising groups e, f and g were 2 to 6 years of age. The animals were weighed to the nearest .1 kilograms. Udders were excised, stripped of hide and teats and weighed to the nearest gram. They were trimmed of lymph nodes, blood vessels and excess fat before being reweighed. Small samples were excised and immersed into Bouin's solution for subsequent histological sectioning (Carleton and Drury, 1957). Other small samples were obtained for protein determination by the Kjeldahl method. The remaining tissue was frozen at --10 C until subsequent lipid extraction. This was done by cutting the glands into small pieces and immersing into a 2:1 mixture of chloroform:methanol (2 liters per kilogram wet mammary weight). After two changes, the tissues were transferred to a 3:1 mixture of ethanol:ether, with four changes required before lipid extraction was complete. The dried fat-free tissue (DFFT) was weighed and ground to a fine powder. One hundred milligram aliquots of the D F F T were weighed for subsequent chemical determinations of DNA by the method of Webb and Levy (1955) and RNA by the orcinol method (A1baum and Umbreit, 1947). Data accumulated and analyzed for each group included body weight, untrimmed mammary weight, trimmed mammary weight, D F F T weight, total protein, total DNA, DNA/kg body weight, total RNA, RNA/kg body weight and RNA/DNA ratio. DFFT, protein and nucleic acids were also expressed as percents of trimmed wet weight. Statistical analysis was accomplished by comparing two means using Student's t test (Kempthorne, 1957). R ESU LTS
Body weights of female sheep ranged from 5.5 kg near birth to 49.7 kg at the beginning of
pregnancy. All lambs were born in early September, 1973. Lambs were weaned one week prior to slaughter of the 3-month-old group, which had a mean body weight of 24.4 kilograms. Lambs were fattened on grass only and gained to 26.4 kg at 4 months and 29.9 kg at 5 months of age. The group of ewes slaughtered at 140 to 148 days of pregnancy had actual body weights averaging 53.5 kg, but 6.0 kg was
119
subtracted to allow for the weight of the lamb, placental fluids and membranes. With this correction there was no significant difference in weight between pregnant cases and postpartum ewes (table 1). Mammary gland wet weights varied from 11 g in fetuses near birth to 1,327 g at 5 days of lactation. Significant differences were found between the fetal glands and those in 3-, 4- and 5-month-old lambs, between the lambs and the beginning of pregnancy, between the beginning and end of pregnancy and between the end of pregnancy and day 5 of lactation (P
GLAND
GROWTH
IN S H E E W
R. R. Anderson 2 ,3 Ruakura A n i m a l Researcb Centre, Hamilton, New Zealand and University o f Missouri 4 , Columbia 65201
SUMMARY
INTRODUCTION
Development of m a m m a r y glands was assessed in Romney and Romney-cross sheep. Animals were slaughtered at birth + or - 5 days, at 3, 4 and 5 months, at the beginning of pregnancy (2 to 3 days after mating), at the end of pregnancy (140 to 148 days pregnant) and at 5 days lactation. Mammary glands were weighed before and after trimming and the trimmed glands were extracted with lipid solvents. The remaining dried fat-free tissue (DFFT) were weighed and ground. Nucleic acids and nitrogen were measured. Based upon wet weight changes, 25% of growth occurred prior to pregnancy, 55% during pregnancy and 20% during early lactation. When DFFT was evaluated, the increases were 20% from birth to the beginning of pregnancy, 80% during pregnancy and none in early lactation. Percent protein paralleled DFFT changes among groups. However, when DNA, the most realistic measure of mammary growth, was considered, the percentages of development were 20% from birth to the start of pregnancy, 78% during pregnancy and 2% during early lactation. The ratio of RNA to DNA remained near 1 from 3 months of age to the end of pregnancy and increased to 1.7 in early lactation. Unlike many small laboratory species, the sheep does not experience any appreciable post-parturient 'lactational' growth of the mammary gland.
Growth of mammary glands in mammals has been measured by anatomical and biochemical methods with reasonable success. Relative amounts of growth during various phases in the female's development have been determined in several laboratory species in order to establish bases for experimentation of hormonal stimuli concerned in mammary gland growth. Those studies which have incorporated in them the determination of nucleic acids as indices of mammary cell numbers and relative cellular activity have included mice (Brookreson and Turner, 1961), hamsters (Sinha et al., 1970) and rabbits (Lu and Anderson, 1973). Limited research has been directed toward domestic species, including cattle (Tucker et al., 1973), swine (Hacker and Hill, 1972) and sheep (Denamur et al., 1972), in which nucleic acid changes during early lactation were studied. The present study considers mammary gland growth in sheep from birth, through puberty and pregnancy, to early lactation with the aim of establishing a basis for recommendations in management and nutrition, as well as experimentally stimulating mammary growth by various hormone regimes.
(Key Words: Mammary Gland, Growth, Sheep.)
MATERIALS AND METHODS Female sheep of the Romney breed or Romney-crosses with Southdowns or Border Leichesters were used in this study. They were taken to the abattoir at Ruakura Animal Research Centre and slaughtered. Groups and numbers per group were as follows:
1Contribution from the Missouri Agricultural Exa. fetuses from 140 to 148 days pregnancy periment Station. Journal Series No. 7111. Approved or lambs 5 days old (n = 10) by the Director. 2Work conducted while author was a Senior b. 3-month-old lambs (n = 30) Fulbright Research Fellow in New Zealand. c. 4-month-old lambs (n = 30) 3The author expresses his gratitude to W. G. d. 5-month-old lambs (n = 27) Whittlestone for use of his laboratory and to A. e. beginning (day 2 to 3) of pregnancy (n = Pearson and R. Findlay for their assistance. 4Department of Dairy Husbandry. 20) 118 JOURNAL OF ANIMAL SCIENCE, Vol. 41, No. 1, 1975
Downloaded from https://academic.oup.com/jas/article-abstract/41/1/118/4668118 by Washington University in St. Louis user on 06 August 2018
MAMMARY GLAND GROWTH IN SHEEP f. late (day 140 to 148) pregnancy (n = 19) g. early (day 5) lactation (n = 17). Ewes comprising groups e, f and g were 2 to 6 years of age. The animals were weighed to the nearest .1 kilograms. Udders were excised, stripped of hide and teats and weighed to the nearest gram. They were trimmed of lymph nodes, blood vessels and excess fat before being reweighed. Small samples were excised and immersed into Bouin's solution for subsequent histological sectioning (Carleton and Drury, 1957). Other small samples were obtained for protein determination by the Kjeldahl method. The remaining tissue was frozen at --10 C until subsequent lipid extraction. This was done by cutting the glands into small pieces and immersing into a 2:1 mixture of chloroform:methanol (2 liters per kilogram wet mammary weight). After two changes, the tissues were transferred to a 3:1 mixture of ethanol:ether, with four changes required before lipid extraction was complete. The dried fat-free tissue (DFFT) was weighed and ground to a fine powder. One hundred milligram aliquots of the D F F T were weighed for subsequent chemical determinations of DNA by the method of Webb and Levy (1955) and RNA by the orcinol method (A1baum and Umbreit, 1947). Data accumulated and analyzed for each group included body weight, untrimmed mammary weight, trimmed mammary weight, D F F T weight, total protein, total DNA, DNA/kg body weight, total RNA, RNA/kg body weight and RNA/DNA ratio. DFFT, protein and nucleic acids were also expressed as percents of trimmed wet weight. Statistical analysis was accomplished by comparing two means using Student's t test (Kempthorne, 1957). R ESU LTS
Body weights of female sheep ranged from 5.5 kg near birth to 49.7 kg at the beginning of
pregnancy. All lambs were born in early September, 1973. Lambs were weaned one week prior to slaughter of the 3-month-old group, which had a mean body weight of 24.4 kilograms. Lambs were fattened on grass only and gained to 26.4 kg at 4 months and 29.9 kg at 5 months of age. The group of ewes slaughtered at 140 to 148 days of pregnancy had actual body weights averaging 53.5 kg, but 6.0 kg was
119
subtracted to allow for the weight of the lamb, placental fluids and membranes. With this correction there was no significant difference in weight between pregnant cases and postpartum ewes (table 1). Mammary gland wet weights varied from 11 g in fetuses near birth to 1,327 g at 5 days of lactation. Significant differences were found between the fetal glands and those in 3-, 4- and 5-month-old lambs, between the lambs and the beginning of pregnancy, between the beginning and end of pregnancy and between the end of pregnancy and day 5 of lactation (P
