ABSTRACT The growth and importance of the Brazilian citrus industry in the world involves the introduction of technologies such as the use of plant growth regulators such as gibberellic acid (GA3). The effects of doses of 0, 5, 10 and 15 mg L-1 of GA3 (Pro-Gibb®) associated with the surfactant Silwett L-77® at 0.5 mL L-1 were evaluated in an experiment by spraying the plants of a ‘Natal’ orange orchard in the Northern region of the state of São Paulo, Brazil. The treatments were applied annually, for two years, when the fruits were still fully green, but before the flowering of the next crop. The results showed, at the picking period, that the treatment of ‘Natal’ sweet orange trees with gibberellic acid associated with silicone surfactant, reduced fruit abscission due to the higher force needed to detach the fruits from the plants and significantly increased the peel resistance to puncture; The maintenance of the greener color of the orange peel, evaluated using a colorimeter, make them less attractive to fruit flies and make it possible the delay on insecticides treatments for flies control. Additionally, it allows the delay on harvesting by storing the fruits on the plants, with staggered harvest beyond the normal period for the variety. It is suggested doses of 5 to 10 mg L-1 GA3 always associated to silicone surfactant (0.05% L77) to obtain the best responses in oranges of Natal cultivar. Treatments with GA3 did not affect the productivity of the ‘Natal’ sweet orange orchard, neither the maturation and nor the technological quality of the fruits.

RESUMO O crescimento e importância da citricultura brasileira no mundo passa pela introdução de tecnologias como a utilização de reguladores vegetais como o ácido giberélico (GA3). Os efeitos das doses de 0, 5, 10 e 15 mg L-1 de GA3 (Pro-Gibb®) associado ao surfactante Silwett L-77® a 0,5 mL L-1 foram avaliadas em experimento pulverizando as plantas de um pomar de laranjeira ‘Natal’ na região Norte do estado de São Paulo, Brasil. A aplicação dos tratamentos deu-se anualmente, durante dois anos, quando os frutos ainda estavam totalmente verdes, porém antes do florescimento da próxima safra. Os resultados mostraram por ocasião da colheita que o tratamento das laranjeiras ‘Natal’ com ácido giberélico associado a surfactante siliconado, diminuiu a abscisão de frutos pela maior força necessária para destacar os frutos das plantas durante a colheita e aumentou significativamente a resistência da casca à punctura. A manutenção da coloração mais esverdeada da casca dos frutos, avaliada através de colorímetro, os tornam menos atrativo às moscas das frutas e assim possibilita retardar as aplicações de inseticidas para controle das moscas. Além disso, permite retardar as colheitas armazenando os frutos nas plantas, com colheitas escalonadas para além do período normal para a variedade. Sugere-se doses de 5 a 10 mg L-1 GA3 sempre associado a surfactante siliconado (0,05% L77) para se obter as melhores respostas em laranjas da variedade Natal. Os tratamentos com GA3 não afetaram a produtividade do pomar de laranja ‘Natal’, nem a maturação e nem a qualidade tecnológica dos frutos.

The objective of the present study was to evaluate the genetic and non-genetic effects that influence vigor at birth and preweaning mortality in Nellore calves. A total of 11,727 records of births that occurred between 1978 and 2006, offspring of 363 sires, were analyzed. Poor calf vigor at birth (VB) and preweaning mortality divided into stillbirth (SB), early mortality (EM) and total mortality (TM) were analyzed as binary variables. Generalized linear models were used for the evaluation of non-genetic effects and generalized linear mixed models for genetic effects (sire and animal models). The incidences were 4.75% for VB, 2.66% for SB, 5.28% for EM, and 7.99% for TM. Birth weight was the effect that most influenced the traits studied. Calves weighing less than 22 kg (females) and less than 24 kg (males) were at a higher risk of low vigor and preweaning mortality. Preweaning mortality was higher among calves born from cows aged <3 and >11 years at calving compared with cows aged 7 to 10 years. Male calves presented less vigor and higher preweaning mortality than female calves. Selection for postweaning weight did not influence preweaning mortality. The heritability estimates ranged between 0.01 and 0.09 for VB, 0.00 and 0.27 for SB, 0.03 and 0.17 for EM and 0.02 and 0.10 for TM. Stillbirth should be included as a selection criterion in breeding programs of Nellore cattle, alone or as part of a selection index, aiming to reduce preweaning mortality.

Em decorrência da elevada ocorrência (18%) de bezerros Guzerá que não mamaram por conta própria em suas mães (falha na primeira mamada), foram avaliados os fatores associados a estas falhas, sua influência na mortalidade e parâmetros genéticos para falha na primeira mamada (FPM). Dos 1.527 bezerros Guzerá nascidos de 1992 a 2004, 279 apresentaram FPM. Os efeitos fixos foram estudados utilizando o procedimento GENMOD-SAS com função de ligação probit. Parâmetros genéticos para FPM foram estimados por máxima verossimilhança restrita aproximada, ajustando modelo animal que incluiu efeitos genéticos diretos e maternos e de ambiente permanente da vaca. Verificou-se que os principais fatores predisponentes à FPM foram vacas com problema de úbere e tetos e bezerros pesando menos de 25 kg ao nascimento. FPM influenciou a mortalidade, com maior chance de óbitos para bezerros que falharam em comparação aos que mamaram naturalmente. A estimativa de herdabilidade do efeito materno foi baixa (0,08) e a referente ao efeito direto, nula. A estimativa de repetibilidade também foi baixa (0,17). Devido ao impacto de FPM na mortalidade de bezerros, sugere-se que a avaliação da conformação do aparelho mamário seja utilizada como um indicador para minimizar o problema. Entretanto, a baixa magnitude da estimativa de herdabilidade indica que progresso genético mediante seleção contra FPM poderia ser obtido somente a longo prazo.

This study aimed to evaluate the effects related to the high occurrence (18%) of Guzerá newborn calves that failed to suckle (FS) after birth. Data from 1527 births recorded from 1992 to 2004 were analyzed by a fixed effects model using the probit linking function with the GENMOD procedure of SAS®. An animal model including direct and maternal additive genetic and cow permanent environment effects was also used to estimate genetic parameters for FS by quasi-restricted maximum likelihood. Cows with udder and teat problems and calves weighting less than 25 kg at birth were the major effects associated to the occurrence of FS in newborn calves which were more susceptible to mortality than those that successfully suckled. Maternal and direct effects heritability estimates for FS were respectively 0.08 and null. The repeatability estimate for FS was 0.17. The evaluation of the conformation of the cow mammary system may be used as an indicator to minimize the occurrence of FS. Genetic progress by selection for reducing FS in Guzerá newborn calves may be expected only in the long term.