The number of dairy cattle in Jersey reduced by more than 500 last year, a decrease of 15%, government statistics have shown.
It meant the amount of milk produced fell from 13.3 to 11.8 million litres (2.9 to 2.6 million gallons).
Jersey Royal potato exports were also down in 2008 by 11% compared with the previous year.
The politician responsible for agriculture warned of making judgements on one year's figures.
The latest statistics, issued by the Environmental Management and Rural Economy section, said there were 3,571 dairy cattle in Jersey in 2007 which fell to 3,050 in 2008.
The figures also show that 28,706 tonnes of Jersey Royals were exported last year, down more than 3,600 tonnes on 2007.
'Full of confidence'
The department said it was due to some wetter than average months in the first half of the year and frosts.
Although the volume of potatoes exported fell, for the first time in five years, the area of farmland used to grow potatoes increased.
Higher production costs and static returns from UK retailers saw "practically the end" of the greenhouse-grown tomato and pepper export market, the department said.
Constable Len Norman, the States member responsible for agriculture, said he was unconcerned about the figures.
The agriculture industry is full of confidence at the moment, he told BBC Jersey.
He warned of making judgements based on just one year's figures because the industry can be impacted by market conditions and the weather, which vary each year.