WESTBROOK — Idexx Laboratories Inc., which makes diagnostic products for veterinarians and tests for livestock and poultry, on Tuesday posted higher second-quarter profits but its stock dropped after it lowered its full-year revenue guidance again.

Second-quarter profits totaled $54 million, or 99 cents per share, up from $51.3 million, or 91 cents per share, a year ago.

The results topped Wall Street analysts’ average earnings expectations of 97 cents a share, according to FactSet.

Quarterly revenue rose 5 percent to $352.6 million from $335.6 million, driven by growth in its pet group. The pet group, known as the companion animal group, had revenues of $295.8 million, up from $278.3 million a year ago.

Sales in the water-testing business rose slightly to $22.4 million from $22.0 million, while sales in the livestock, poultry and dairy sector fell slightly to $28.3 million from $28.6 million a year ago.

For the full year, the Westbrook-based company again cut its full-year guidance, citing increased share repurchases, lower organic revenue growth and unfavorable changes in foreign currency exchange rates.

Idexx now expects to earn $3.42 to $3.48 per share for 2013, compared with a prior range of $3.40 to $3.46. Revenue is expected to be in the range of  $1.37 billion to $1.38 billion, down from its previous forecast of $1.38 billion to $1.39 billion. The company had already trimmed its 2013 outlook earlier this year.

Analysts, on average, expect full-year earnings per share of $3.44 and revenue of $1.38 billion, according to FactSet.

Shares of Idexx fell $1.05 Tuesday, closing at $96.37 on the Nasdaq stock exchange.