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Bortolozzo FP, Zanin GP, Christ TS, Rech RD, da Rosa Ulguim R, Mellagi APG. Artificial insemination and optimization of the use of seminal doses in swine. Anim Reprod Sci 2024:107501. [PMID: 38782677 DOI: 10.1016/j.anireprosci.2024.107501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2024] [Revised: 05/14/2024] [Accepted: 05/16/2024] [Indexed: 05/25/2024]
Abstract
The optimization of processes associated with artificial insemination (AI) is of great importance for the success of the pig industry. Over the last two decades, great reproductive performance has been achieved, making further significant progress limited. Optimizing the AI program, however, is essential to the pig industry's sustainability. Thus, the aim is not only to reduce the number of sperm cells used per estrous sow but also to improve some practical management in sow farms and boar studs to transform the high reproductive performance to a more efficient program. As productivity is mainly influenced by the number of inseminated sows, guaranteeing a constant breeding group and with healthy animals is paramount. In the AI studs, all management must ensure conditions to the health of the boars. Some strategies have been proposed and discussed to achieve these targets. A constant flow of high-quality and well-managed breeding groups, quality control of semen doses produced, more reliable technology in the laboratory routine, removal of less fertile boars, the use of intrauterine AI, the use of a single AI with control of estrus and ovulation (fixed-time AI), estrus detection based on artificial intelligence technologies, and optimization regarding the use of semen doses from high genetic-indexed boars are some strategies in which improvement is sought. In addition to these new approaches, we must revisit the processes used in boar studs, semen delivery network, and sow farm management for a more efficient AI program. This review discusses the challenges and opportunities in adopting some technologies to achieve satisfactory reproductive performance and efficiency.
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Affiliation(s)
- Fernando Pandolfo Bortolozzo
- Department of Animal Medicine, Veterinary Faculty, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, Avenida Bento Gonçalves, 9090, Porto Alegre, RS CEP 91540-000, Brazil.
| | - Gabriela Piovesan Zanin
- Department of Animal Medicine, Veterinary Faculty, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, Avenida Bento Gonçalves, 9090, Porto Alegre, RS CEP 91540-000, Brazil
| | - Thaís Spohr Christ
- Department of Animal Medicine, Veterinary Faculty, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, Avenida Bento Gonçalves, 9090, Porto Alegre, RS CEP 91540-000, Brazil
| | - Rodrigo Dalmina Rech
- Department of Animal Medicine, Veterinary Faculty, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, Avenida Bento Gonçalves, 9090, Porto Alegre, RS CEP 91540-000, Brazil
| | - Rafael da Rosa Ulguim
- Department of Animal Medicine, Veterinary Faculty, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, Avenida Bento Gonçalves, 9090, Porto Alegre, RS CEP 91540-000, Brazil
| | - Ana Paula Gonçalves Mellagi
- Department of Animal Medicine, Veterinary Faculty, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, Avenida Bento Gonçalves, 9090, Porto Alegre, RS CEP 91540-000, Brazil
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Islas-Fabila P, Roldán-Santiago P, de la Cruz-Cruz LA, Limón-Morales O, Dutro-Aceves A, Orozco-Gregorio H, Bonilla-Jaime H. Importance of Selected Nutrients and Additives in the Feed of Pregnant Sows for the Survival of Newborn Piglets. Animals (Basel) 2024; 14:418. [PMID: 38338061 PMCID: PMC10854669 DOI: 10.3390/ani14030418] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Revised: 01/22/2024] [Accepted: 01/23/2024] [Indexed: 02/12/2024] Open
Abstract
This systematic review analyzed the effect of selected nutrients and additives in the feed of pregnant sows on the survival of newborn piglets. We analyzed 720 peer-reviewed publications in English in PubMed® and Web of Science®, dated July 2023 to January 2024, related to the effect of dietary supplementation with fatty acids and various percentages of protein, amino acids, and/or sources of dietary fiber on the offspring of gestating sows. While several papers evaluated the effect of nutrition on gestating sows, only a few delved into the distinct feeding strategies required at each stage of gestation to meet the NRC's nutritional requirements for maternal tissue gain and postnatal neonatal survival and growth. This body of research suggests that as gestation progresses the sow's nutritional requirements increase, as the NRC established, to satisfy their own metabolic needs and those of their fetuses. Additional research is needed to determine an optimal feeding strategy.
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Affiliation(s)
- Paloma Islas-Fabila
- Programa de Doctorado en Ciencias Biológicas y de la Salud, Universidad Autónoma Metropolitana, Unidad Iztapalapa, Mexico City 09340, Mexico;
| | - Patricia Roldán-Santiago
- Departamento de Reproducción, Facultad de Medicina Veterinaria y Zootecnia, Universidad Nacional Autónoma de México, Avenida Universidad, Mexico City 04510, Mexico
| | - Luis Alberto de la Cruz-Cruz
- Escuela de Medicina Veterinaria y Zootecnia, Universidad del Valle de México-Coyoacán, Calzada de Tlalpan, Mexico City 04910, Mexico; (L.A.d.l.C.-C.); (A.D.-A.)
- Departamento de Producción Agrícola y Animal, Universidad Autónoma Metropolitana, Unidad Xochimilco, Calzada del Hueso 1100, Coapa, Villa Quietud, Coyoacán, Mexico City 04960, Mexico;
| | - Ofelia Limón-Morales
- Departamento de Biología de la Reproducción, Universidad Autónoma Metropolitana, Unidad Iztapalapa, Mexico City 09340, Mexico;
| | - Anna Dutro-Aceves
- Escuela de Medicina Veterinaria y Zootecnia, Universidad del Valle de México-Coyoacán, Calzada de Tlalpan, Mexico City 04910, Mexico; (L.A.d.l.C.-C.); (A.D.-A.)
| | - Héctor Orozco-Gregorio
- Departamento de Producción Agrícola y Animal, Universidad Autónoma Metropolitana, Unidad Xochimilco, Calzada del Hueso 1100, Coapa, Villa Quietud, Coyoacán, Mexico City 04960, Mexico;
| | - Herlinda Bonilla-Jaime
- Departamento de Biología de la Reproducción, Universidad Autónoma Metropolitana, Unidad Iztapalapa, Mexico City 09340, Mexico;
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Bortolozzo FP, Zanin GP, Ulguim RDR, Mellagi APG. Managing Reproduction in Hyperprolific Sow Herds. Animals (Basel) 2023; 13:1842. [PMID: 37889779 PMCID: PMC10252095 DOI: 10.3390/ani13111842] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Revised: 05/26/2023] [Accepted: 05/30/2023] [Indexed: 10/29/2023] Open
Abstract
The rearing of large litters from hyperprolific sows is a characteristic of modern genotypes. However, these sows have body and reproductive characteristics that differentiate them from the genotypes of the past decades, making it necessary to adopt different management strategies. This review describes the main care and challenges associated with the hyperprolificity of sows during the period in which replacement gilts are selected, along with gestation, parturition, lactation, and the weaning-estrus interval. It describes the challenges that these sows' piglets will face during the lactation period and includes some strategies adopted to develop these surplus piglets. In addition, it identifies areas where more research is needed to understand the reproductive management of modern genotypes.
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Affiliation(s)
- Fernando Pandolfo Bortolozzo
- Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul (UFRGS), Setor de Suínos, Porto Alegre 90540-000, RS, Brazil
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Nevrkla P, Lujka J, Kopec T, Horký P, Filipčík R, Hadaš Z, Střechová V. Combined Effect of Sow Parity and Terminal Boar on Losses of Piglets and Pre-Weaning Growth Intensity of Piglets. Animals (Basel) 2021; 11:ani11113287. [PMID: 34828018 PMCID: PMC8614461 DOI: 10.3390/ani11113287] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2021] [Revised: 11/11/2021] [Accepted: 11/15/2021] [Indexed: 11/16/2022] Open
Abstract
This study analysed the effect of sow parity (P), terminal boars (TB), and their combination on reproductive parameters of sows, losses of piglets, and their individual live-weight (LW) and average daily gain (ADG) from birth to weaning. A total of 120 sows of Large White × Landrace hybrid combination from the first to the fourth parity (30 sows per parity) were included in the observation. The sows were inseminated by terminal boars of Pietrain (Pn), Large Whitesireline (LWSL), and Duroc (D) breeds and Duroc × Large Whitesirelinie (D × LWSL), Large Whitesirelinie × Pietrain (LWSL × Pn), and Duroc × Pietrain (D × Pn) hybrid combinations (20 sows per terminal boar population). The results proved a significant effect of P on the total numbers of piglets (TN), the numbers of stillborn piglets (SB), and the pre-weaning losses of piglets (L) (p ≤ 0.01) with the lowest losses found in the third parity sows. A significant effect of TB was confirmed for TN, the numbers of live-born piglets (LB), SB, the numbers of mummified piglets (M) and non-viable piglets (N), and (L) (p ≤ 0.01). The sows inseminated by D and LWSL boars showed the lowest total numbers of piglets but also the highest survivability of piglets until weaning. Significant effects of interaction between P and TB were observed for the TN, SB, N, and L (p ≤ 0.05). Evaluation of growth parameters in piglets (n = 1547) showed that P significantly influenced LW in the first three weeks of life (p ≤ 0.01) and ADG from birth to Day 7 and from Day 15 to Day 21 (p ≤ 0.01). Additionally, a significant effect (p ≤ 0.01) of TB was proven on individual weight and ADG in all the observed time intervals, with the highest growth found in the piglets of the D and LWSL boars. Significant interactions (p ≤ 0.01) between P and TB were found for LW and ADG in all the time intervals.
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Affiliation(s)
- Pavel Nevrkla
- Department of Animal Breeding, Faculty of AgriSciences, Mendel University in Brno, Zemědělská 1, 613 00 Brno, Czech Republic; (J.L.); (T.K.); (R.F.); (Z.H.); (V.S.)
- Correspondence:
| | - Jan Lujka
- Department of Animal Breeding, Faculty of AgriSciences, Mendel University in Brno, Zemědělská 1, 613 00 Brno, Czech Republic; (J.L.); (T.K.); (R.F.); (Z.H.); (V.S.)
| | - Tomáš Kopec
- Department of Animal Breeding, Faculty of AgriSciences, Mendel University in Brno, Zemědělská 1, 613 00 Brno, Czech Republic; (J.L.); (T.K.); (R.F.); (Z.H.); (V.S.)
| | - Pavel Horký
- Department of Animal Nutrition and Forage Production, Faculty of AgriSciences, Mendel University in Brno, Zemědělská 1, 613 00 Brno, Czech Republic;
| | - Radek Filipčík
- Department of Animal Breeding, Faculty of AgriSciences, Mendel University in Brno, Zemědělská 1, 613 00 Brno, Czech Republic; (J.L.); (T.K.); (R.F.); (Z.H.); (V.S.)
| | - Zdeněk Hadaš
- Department of Animal Breeding, Faculty of AgriSciences, Mendel University in Brno, Zemědělská 1, 613 00 Brno, Czech Republic; (J.L.); (T.K.); (R.F.); (Z.H.); (V.S.)
| | - Vendula Střechová
- Department of Animal Breeding, Faculty of AgriSciences, Mendel University in Brno, Zemědělská 1, 613 00 Brno, Czech Republic; (J.L.); (T.K.); (R.F.); (Z.H.); (V.S.)
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Altrenogest treatment during the last week of lactation on ovarian traits and subsequent reproductive performance of primiparous and multiparous sows. Theriogenology 2021; 176:122-127. [PMID: 34601236 DOI: 10.1016/j.theriogenology.2021.09.027] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Revised: 09/24/2021] [Accepted: 09/25/2021] [Indexed: 12/29/2022]
Abstract
High-quality follicles result in larger corpora lutea (CL), producing more progesterone, and having a fundamental role in pregnancy maintenance. For some sows, follicular growth takes place during lactation, and follicle selection occurs under a catabolic environment. As altrenogest inhibits follicular development, this study aimed to evaluate follicular growth, CL size, estrus expression, and subsequent reproductive performance of sows treated with altrenogest during the last seven days of a three-week lactation. A total of 81 primiparous and 319 multiparous sows were allocated to two treatments: CONT (control group) and ALT (20 mg of altrenogest/day during the last seven days of lactation). Subsamples of 20 primiparous sows and 97 multiparous were randomly selected to evaluate follicular growth and 26 multiparous sows for serum progesterone analysis at day 21 of gestation. On day 21 of pregnancy, CL measurement was performed by ultrasound. Once in estrus, sows were post-cervically inseminated with pooled semen doses with 1.5 × 109 sperm cells at estrus onset and every 24 h during the standing reflex period. Sows not showing estrus until 10 days after weaning were considered in anestrus. The variables weaning-to-estrus interval, CL size, litter size in the subsequent cycle, and piglet birth weight were evaluated using the GLIMMIX procedure and compared using the Tukey-Kramer test. Anestrus, pregnancy, farrowing, and adjusted farrowing rate were evaluated as binary responses using logistic regression. Follicular size was analyzed as a repeated measure during treatment and after weaning. Treatment was considered as a fixed effect. During the treatment period, follicular size was smaller in ALT sows than CONT sows (3.29 vs. 3.52 mm; P < 0.001). However, after treatment, ALT sows showed a larger follicular size than CONT sows (5.30 vs. 5.03 mm; P ≤ 0.01). There were less ALT sows showing estrus than CONT sows on days three (1.03 vs. 4.57%) and four (55.38 vs. 68.02%) after weaning (P ≤ 0.05), respectively. At 21 days after insemination, ALT sows showed larger CL size and lower CL size variation (P < 0.01) than CONT sows. Anestrus rate, pregnancy rate, farrowing rate, adjusted farrowing rate, litter size in the subsequent cycle, piglet birth weight, litter birth weight, and birth weight variation did not differ between treatments (P ≥ 0.14). In conclusion, altrenogest treatment during the last week of lactation concentrated estrus expression on day five after weaning, larger follicle and CL sizes; however, with no improvement in reproductive performance.
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Sow-related factors affecting the postweaning feed intake in Landrace × Large White females. Trop Anim Health Prod 2021; 53:261. [PMID: 33860367 DOI: 10.1007/s11250-021-02720-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2021] [Accepted: 04/12/2021] [Indexed: 10/21/2022]
Abstract
During the weaning-to-estrus interval (WEI), a high feeding level is usually offered to recover losses due to lactational catabolism. However, several factors can affect the appetite, possibly impairing the efficacy of this strategy. This study aimed to investigate the effect of sow-related factors on average daily feed intake (ADFI) during WEI in 142 primiparous and 458 multiparous sows. After weaning, the sows received 4.3 kg/day of feed and the wastage was recorded. The ADFI after weaning was lower in primiparous than multiparous sows, and on estrous day than in 2 and 3 days preceding estrus (P ≤ 0.05). In primiparous sows, lower ADFI was observed if they had higher backfat thickness at 112 days of gestation (BFT ≥ 11.5 mm) or higher reserves at weaning (BFT ≥ 10.5 mm, caliper units ≥ 12 or ≥ 157 kg; P ≤ 0.05). Higher body reserves at the end of gestation (caliper units ≥ 12, BFT ≥ 11.0 mm, or BCS ≥ 3.0) or weaning (caliper units ≥ 13, BFT ≥ 12.5 mm) negatively affected the ADFI in multiparous sows (P < 0.04). Weaned litter size ≤ 11 piglets (P = 0.06) and shorter lactation length (P< 0.01) decreased the ADFI in primiparous sows. Greater loss in caliper units during lactation tended to reduce ADFI in primiparous and multiparous sows (P ≤ 0.07). Multiparous sows with greater losses in BFT and BCS had lower ADFI (P ≤ 0.03). The ADFI during WEI is reduced when sows are in estrus or if they have greater body reserves.
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Calabrò S, Vastolo A, Musco N, Lombardi P, Troisi A, Polisca A, Vallesi E, Orlandi R, Cutrignelli MI. Effects of Two Commercial Diets on Several Reproductive Parameters in Bitches: Note Two-Lactation and Puppies' Performance. Animals (Basel) 2021; 11:ani11010173. [PMID: 33450854 PMCID: PMC7828350 DOI: 10.3390/ani11010173] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2020] [Revised: 01/05/2021] [Accepted: 01/10/2021] [Indexed: 11/16/2022] Open
Abstract
The study aimed to compare two diets, Control (CTR) and Experimental (EX) (mainly differing as regards their ingredients, energy, and protein contents) administered to medium and large-sized bitches from two months before the expected proestrus and up to 30 days after delivery on mothers' weight, body condition score, litter size, milk quality, and puppies' growth. No differences were found for body weight during pregnancy, even if the BCS after delivery was significantly (p < 0.01) higher in the EX group than in the CTR one. Concerning the size effect, the percentage of weight gain on the initial body weight was double in medium-sized dogs compared to large dogs (p < 0.01). The number of puppies per litter was significantly higher (p < 0.05) for the EX group compared to the CTR one. Concerning puppies' weight, the CTR group showed a significantly (p < 0.01) higher body weight from the 21st day of life due to the significant (p < 0.01) higher daily weight gain during the suckling period. Considering the performance of bitches and puppies, both diets seem useful for these stages of their lives. In fact, after 30 days of lactation, all tested bitches showed a healthy status and both the percentage of newborns mortality and puppies' growth kinetics fell into the normal physiological range for the species.
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Affiliation(s)
- Serena Calabrò
- Department of Veterinary Medicine and Animal Production, University of Napoli Federico II, 80137 Napoli, Italy; (S.C.); (A.V.); (P.L.); (M.I.C.)
| | - Alessandro Vastolo
- Department of Veterinary Medicine and Animal Production, University of Napoli Federico II, 80137 Napoli, Italy; (S.C.); (A.V.); (P.L.); (M.I.C.)
| | - Nadia Musco
- Department of Veterinary Medicine and Animal Production, University of Napoli Federico II, 80137 Napoli, Italy; (S.C.); (A.V.); (P.L.); (M.I.C.)
- Correspondence:
| | - Pietro Lombardi
- Department of Veterinary Medicine and Animal Production, University of Napoli Federico II, 80137 Napoli, Italy; (S.C.); (A.V.); (P.L.); (M.I.C.)
| | - Alessandro Troisi
- School of Bioscience and Veterinary Medicine, University of Camerino, 62024 Matelica, Italy;
| | - Angela Polisca
- Department of Veterinary Medicine, University of Perugia, 06124 Perugia, Italy;
| | - Emanuela Vallesi
- Tyrus Veterinary Clinic, Via A. Bartocci 1/G, 05100 Terni, Italy; (E.V.); (R.O.)
| | - Riccardo Orlandi
- Tyrus Veterinary Clinic, Via A. Bartocci 1/G, 05100 Terni, Italy; (E.V.); (R.O.)
| | - Monica I. Cutrignelli
- Department of Veterinary Medicine and Animal Production, University of Napoli Federico II, 80137 Napoli, Italy; (S.C.); (A.V.); (P.L.); (M.I.C.)
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Mallmann AL, Arend LS, Oliveira GS, Mellagi APG, Ulguim RR, Bernardi ML, Bortolozzo FP, Knox RV. Effects of flush feeding strategy before breeding on reproductive performance of modern replacement gilts: impacts on ovulation rate and litter traits. J Anim Sci 2020; 98:skaa186. [PMID: 32506131 PMCID: PMC7447920 DOI: 10.1093/jas/skaa186] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2020] [Accepted: 06/03/2020] [Indexed: 11/12/2022] Open
Abstract
AbstractThe effects of two feed levels offered during two estrous cycles before insemination were evaluated on the reproductive performance of gilts. A total of 93 gilts (PIC Hendersonville, TN) were individually housed and manually fed twice a day with 2.1 or 3.6 kg/d of a corn and soybean meal-based diet (3.15 Mcal ME/kg and 0.64% standardized ileal digestible lysine), during two estrous cycles before breeding (cycle 1, between first and second estrus; cycle 2, between second and third estrus). Gilts were weighed at the beginning of the experiment, at second and third estrus, and at slaughter (30.2 ± 1.2 d of gestation). Follicles were counted at second estrus, and the embryo-placental units and the corpora lutea were individually counted, measured, and weighed at slaughter. Gilts fed 3.6 kg/d had greater BW gain during cycle 1 and cycle 2 (P < 0.001; + 9.8 kg and + 10.0 kg, respectively) becoming heavier at second and third estrus (P < 0.001). At second estrus, gilts fed 3.6 kg/d had 1.6 more medium-large follicles (P = 0.074) but no difference in follicle size (P = 0.530) was observed. Gilts fed 3.6 kg/d in cycle 1 or cycle 2 had a greater ovulation rate at third estrus (P < 0.016) than those receiving 2.1 kg/d. Also, 3.6 kg/d in cycle 2 increased early embryo mortality (P = 0.006; 2.3 vs. 1.1 dead embryos) and consequently reduced total embryo survival (P = 0.002; 84.6 vs. 90.1%). Gilts fed 3.6 kg/d during cycle 1 had two more total embryos (P < 0.001; 17.2 vs. 15.1) and two more vital embryos on day 30 (P < 0.001; 16.7 vs. 14.5) in comparison with gilts fed 2.1 kg/d. The coefficient of variation for placental length was greater for gilts fed 3.6 kg/d during cycle 1 (P = 0.003). No further significant effects of feeding levels were observed on embryo and placental traits (P ≥ 0.063). These results suggest that the feeding level during the first cycle after pubertal estrus is crucial to set ovulation rate and potential litter size for breeding at next estrus. However, flush feeding gilts before insemination can negatively impact litter size by reducing embryo survival when breeding at third estrus.
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Affiliation(s)
- André L Mallmann
- Departamento de Medicina Animal/Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil
| | - Lidia S Arend
- Department of Animal Sciences, University of Illinois, Urbana
| | - Gabriela S Oliveira
- Departamento de Medicina Animal/Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil
| | - Ana P G Mellagi
- Departamento de Medicina Animal/Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil
| | - Rafael R Ulguim
- Departamento de Medicina Animal/Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil
| | - Mari L Bernardi
- Departamento de Zootecnia/Faculdade de Agronomia, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil
| | - Fernando P Bortolozzo
- Departamento de Medicina Animal/Faculdade de Veterinária, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil
| | - Robert V Knox
- Department of Animal Sciences, University of Illinois, Urbana
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