Kristen Sejrsen

High body weight gain and reduced bovine mammary growth: physiological basis and implications for milk yield potential

Available evidence concerning the relationship between growth rate, mammary growth and milk yield in heifers leads to these conclusions: 1) Increased growth rate due to high feeding level before puberty onset can lead to reduced pubertal mammary growth and reduced milk yield potential. 2) Increased growth rate due to high feeding level after puberty and during pregnancy have no effect on mammary growth and milk yield. 3) Higher body weight gain due to higher genetic potential for growth is positively related to milk yield. The negative effect of high feeding level before puberty occurs in all breeds, but the level of feeding causing reduced yield varies. Variation in responses between experiments suggests that feeding regimes that support high growth rates without negative effect on yield can be developed. A breakthrough most likely will originate from increased knowledge of the physiological relationship between nutrition and mammary development. Our investigations suggest that blood growth hormone (GH) is important for mammary development, and that the negative effect of high feeding level on mammary development may be due to reduced blood GH. GH, however, does not bind to mammary tissue. Experiments with exogenous GH suggest that GH acts on mammary tissue via IGF-I, but IGF-I is increased by high feeding level - not decreased as GH. This paradoxical relationship cannot be explained by changes in circulating IGF binding proteins. However, the sensitivity of mammary tissue to IGF-I is reduced by high feeding level, probably due to the action of locally produced binding proteins and/or growth factors.

Local IGF-I Axis in Peripubertal Ruminant Mammary Development

The regulation of mammary growth and development in heifers is accomplished by complexinteractions of hormones, growth factors, and extracellular matrix molecules. Many of thesegrowth stimulators are believed to be locally produced in the mammary gland and to beaffected by developmental and nutritional status. Although estrogen and growth hormone areconsidered critical to pubertal mammogenesis, results summarized in this review suggest thatIGF-I6 and IGF binding proteins are especially important locally-produced growth regulatorsin peripubertal ruminants. This assertion is supported by studies of ovariectomized heifers, inwhich increased stromal IGFBP-3 and reduced IGF-I correspond with a failure of udderdevelopment. Similarly, reduced mammary development with overfeeding coincides withreduced mitogenic activity of mammary tissue extracts and altered concentrations of IGF-Iand IGFBPs. In vitro studies convincingly demonstrate that much of the mitogenic activity ofmammary extracts or serum can be attributed to IGF-I and that alterations in IGFBP-3 modulateits effectiveness. Thus by analogy to second messenger mechanisms of action for proteinhormones, local mammary-derived growth factors likely explain many of the effects attributedto the classic mammogenic hormones.

Growth hormone and mammary development

Classic studies in rodents conducted in the 1950s showed that growth hormone (GH) is essential for mammary development both in the pubertal phase and during pregnancy. Since then, a considerable number of experiments have been carried out in ruminants to investigate the role of GH for regulation of normal mammary development and to examine the possibility of enhancing mammary growth by administration of GH. The available evidence demonstrates that GH treatment stimulates mammary growth before puberty, but the data do not convincingly support the idea that the effect is translated into increased milk yield. GH treatment during late pregnancy seems to stimulate both mammary growth and milk yield during lactation. The limited data concerning the effect of GH on mammary growth during lactation indicate that mammary growth is unaffected by GH treatment in early lactation, whereas GH seems to increase the amount of mammary parenchyma in mid-lactation. The mechanism of action of GH remains a puzzle, but the effect of exogenous GH most likely involves insulin-like growth factor-I (IGF-I). Full understanding of the role of endogenous GH for regulation of normal mammary development requires more knowledge about the interaction between GH and IGF-I and the interplay between the GH-IGF-I axis and locally produced factors, including receptors, binding proteins, and growth factors.

The effects of low vs. high concentrate level in the diet on performance in cows milked two or three times daily in early lactation

Abstract The effect of concentrate:forage ratio in the diet and milking frequency on performance was investigated in a 2×2 factorial block design comprising 40 Danish–Holstein dairy cows from parturition to week 16 of lactation. One factor was concentrate level, either low (L: 25% concentrate) or high (H: 75% concentrate), in an ad libitum fed total mixed ration. The second factor was milking frequency, either two or three times daily milking during the first 8 weeks of lactation. From weeks 9 to 16 of lactation, all cows were milked twice daily. During weeks 0 to 8, the cows receiving diet H had a 4.2 units higher net energy intake (Scandinavian feed units), and a 15% higher milk yield compared with the cows receiving diet L. The cows being milked three times a day had an 8% higher daily milk yield, without an increase in DMI, than the cows milked twice a day. In the period from weeks 0 to 8 of lactation, the cows that were fed diet L and milked three times daily mobilised 70 kg, which was 11 to 18 kg more than in the other experimental groups. During weeks 9 to 16 of lactation, the cows receiving diet H maintained a higher feed intake and milk yield similar to that observed in the first 8 weeks of lactation. No positive carry-over effect was seen by changing from three to two milkings a day in early lactation. In conclusion, it seems that cows with high milk yield, achieved by increasing the milking frequency, will benefit from a high concentrate level in the diet.

Mammary gland development in gilts

Mammary development was measured in gilts from birth to day 112 of pregnancy. Non-pregnant gilts were slaughtered at age intervals of approximately 10 days and pregnant gilts were slaughtered at pregnancy stage intervals of approximately 10 days. Before pregnancy, accumulation of mammary tissue and DNA was slow until approximately 90 days of age. The rate of mammary tissue and DNA accretion then increased four- to sixfold. In pregnant gilts, almost all accumulation of mammary tissue and DNA occurred in the last third of pregnancy. The accumulation seemed to continue until term. The measurement of labelled mammary epithelial cells after an in vivo injection of the thymidine analogue bromodeoxyuridine could not detect small or moderate changes in the rate of mammary DNA accumulation. We conclude that mammary gland development in gilts appears to occur in phases with varying rates of mammary growth.

Expression, localization and functional model of cholesterol transporters in lactating and nonlactating mammary tissues of murine, bovine, and human origin

Members of the ATP-binding cassette (ABC) transporters play a pivotal role in cellular lipid efflux. To identify candidate cholesterol transporters implicated in lipid homeostasis and mammary gland (MG) physiology, we compared expression and localization of ABCA1, ABCG1, and ABCA7 and their regulatory genes in mammary tissues of different species during the pregnancy-lactation cycle. Murine and bovine mammary glands (MGs) were investigated during different functional stages. The abundance of mRNAs was determined by quantitative RT-PCR. Furthermore, transporter proteins were localized in murine, bovine, and human MGs by immunohistochemistry. In the murine MG, ABCA1 mRNA abundance was elevated during nonlactating compared with lactating stages, whereas ABCA7 and ABCA1 mRNA profiles were not altered. In the bovine MG, ABCA1, ABCG1, and ABCA7 mRNAs abundances were increased during nonlactating stages compared with lactation. Furthermore, associations between mRNA levels of transporters and their regulatory genes LXRalpha, PPARgamma, and SREBPs were found. ABCA1, ABCG1, and ABCA7 proteins were localized in glandular MG epithelial cells (MEC) during lactation, whereas during nonlactating stages, depending on species, the proteins showed distinct localization patterns in MEC and adipocytes. Our results demonstrate that ABCA1, ABCG1, and ABCA7 are differentially expressed between lactation and nonlactating stages and in association with regulatory genes. Combined expression and localization data suggest that the selected cholesterol transporters are universal MG transporters involved in transport and storage of cholesterol and in lipid homeostasis of MEC. Because of the species-specific expression patterns of transporters in mammary tissue, mechanisms of cholesterol homeostasis seem to be differentially regulated between species.

Biological activity of bovine milk

Abstract The mitogenic activity of milk from different stages of lactation was studied in primary cultures of undifferentiated bovine mammary epithelial cells. The mitogenic activity, measured as DNA synthesis, was 3–4-fold higher in colostrum than in basal medium. The mitogenic activity declined rapidly after calving, and in mid and late lactation the effect was inhibitory, not stimulatory. The content of IGF-I in milk varied with stage of lactation declining from more than 300 ng per ml in colostrum to 1–2 ng per ml in mid lactation and increasing to 20 ng per ml in late lactation. The difference in mitogenic activities between colostrum and mature milk was closely related to the difference in IGF-I content. The changes in IGF-I, however, cannot account for the inhibitory effect of mid and late lactation milk and the difference in the mitogenic effect of colostrum and BPMS (bovine prepartum milk-like secretion). The amounts of IGF binding proteins (24, 28, 34 and 41–44 kDa) in milk followed the same pattern as IGF-I with high content in early lactation and low content in mid lactation. The discrepancies between mitogenic activity and IGF-I content may in some, but not all, cases be related to the content of binding proteins.

Growth, composition and eating quality of Longissimus dorsi from young bulls fed the β-agonist cimaterol at consecutive developmental stages

The objective was to investigate the effect of the β-adrenergic agonist, cimaterol, on gain, composition and meat quality of primerib (M. longissimus dorsi) from Friesian young bulls slaughtered at different developmental stages. Twelve pairs of monozygotic twins were allocated to three liveweight (LW) groups (162, 299 and 407 kg, respectively). Within each pair, one animal was given 0·056 mg cimaterol per kg LW for 90 days, while the other served as a control. Cimaterol treatment increased the estimated gain and the weight of primerib by 55 and 20%, respectively (both P < 0·001), and lean and protein content of the longissimus dorsi muscle by 26 and 25%, respectively (both P < 0·001), and concomitantly reduced fat content of primerib by 16% (P < 0·01) and intramuscular fat in longissimus dorsi by 36% (P < 0·001). Cimaterol treatment reduced total collagen content (P < 0·02), but not collagen solubility (P > 0·55). Meat colour was slightly lighter (lightness, P < 0·06), but pH(24) and pH(final) was not affected by cimaterol. Cimaterol increased Volodkevich shear force values (P < 0·001). In general, the effect of cimaterol on meat quality characteristics was evident in all three LW groups, and LW only affected percent fat in primerib, intramuscular fat content in longissimus dorsi, meat colour and absolute contents of protein, fat and bone.

EFFECT OF FEEDING LEVEL, GRAZING AND FINISHING ON GROWTH AND CARCASS QUALITY OF YOUNG FRIESIAN BULLS

Forty‐one autumn‐born Friesian bull calves were allocated to extensive (E) and intensive (I) production systems. The extensive system included 21 loose‐housed animals fed a roughage‐based diet the first winter, allowing a daily gain of 664 g, followed by a 5‐month grazing period. Ten of these animals were slaughtered directly from pasture (live weight ∼360 kg), and the remaining 11 animals after a further 10‐week finishing period with concentrates in tie‐stalls (live weight ∼460 kg). In the intensive system, animals were housed in tie‐stalls, offered concentrates ad libitum and slaughtered at about 360 kg (n = 11) and 460 kg (n = 9) live weight. Overall, daily gain of E‐bulls was 926 g compared with 1478 g for the I‐bulls (p< 0.001). At pasture, E‐bulls gained 1108 g/day. Compared with I‐bulls of similar live weights, the E‐bulls slaughtered directly from pasture had a lower dressing percentage (p < 0.05), a higher lean content (p < 0.05), a much lower fat content (p < 0.05) and darker meat colour (p < 0....

Alpha-Tocopherol Counteracts the Cytotoxicity Induced by Ochratoxin A in Primary Porcine Fibroblasts

The aims of the current study were to determine the half-lethal concentration of ochratoxin A (OTA) as well as the levels of lactate dehydrogenase release and DNA fragmentation induced by OTA in primary porcine fibroblasts, and to examine the role of α-tocopherol in counteracting its toxicity. Cells showed a dose-, time- and origin-dependent (ear vs. embryo) sensitivity to ochratoxin A. Pre-incubation for 3 h with 1 nM α-tocopherol significantly (P < 0.01) reduced OTA cytotoxicity, lactate dehydrogenase release and DNA damage in both fibroblast cultures. These findings indicate that α-tocopherol supplementation may counteract short-term OTA toxicity, supporting its defensive role in the cell membrane.